Quarry School

Graph each piece only where its condition allows it

Explain it like I am five

Think of laying several sections of road on one map. Each section has its own shape and its own starting and stopping positions. To graph a piecewise function, draw the shape for one formula, then keep it only where its condition allows it. Put all the permitted sections on the same axes. A filled endpoint says the road includes that exact location. A hollow endpoint shows where the shape would go if extended, but that point is absent. At a boundary, a different section may include a point at a different height. Read the assigned height rather than connecting every nearby endpoint.

1213
The included points at inputs 1 and 2 are (1, 1) and (2, 3); the other boundary circles are open.
Reminder
  • Substitution. If f(x) = x2 on the selected branch, f(1) means replace x by 1 and compute 12 = 1.
  • Equality at a boundary. 1 < x ≤ 2 includes 2, while x > 2 does not.
  • Principal square root. If y ≥ 0, y is nonnegative and (−y)2 = y.
Why it works. Graphing the whole formula of every branch can give inputs several competing outputs. Restricting each shape to its branch condition preserves the function's assigned pairs. At a strict boundary, the limiting point can help show where the curve approaches, but it is not part of the graph. The vertical line test counts only included points, so open boundary circles do not create extra outputs. After drawing all pieces, take the union of their horizontal shadows for the domain and their vertical shadows for the range. Different branch ranges may overlap.
RuleDraw each branch only on its assigned interval, using open dots for strict boundaries and closed dots for included ones.
Combine the pieces; domain is the input union and range is the union of reached output heights.
The same idea, five ways
Say it

Say keep the permitted piece and mark whether its endpoint belongs.

Write it

A piecewise graph consists of the formula's points only where its condition allows them.

In math
  • x ≤ 1: draw x2 with a closed endpoint at (1, 1)
  • 1 < x ≤ 2: draw 3 with open (1, 3), closed (2, 3)
  • x > 2: draw x with open (2, 2)
  • Whole domain: {x | x is real} = (−∞, ∞)
  • Whole range: {y | y ≥ 0} = [0, ∞)
Like

Cut unused road sections away before placing the remaining pieces on one map.

See it
1213
The included points at inputs 1 and 2 are (1, 1) and (2, 3); the other boundary circles are open.
The same idea, other ways
As cut-and-keep shapes

Imagine drawing the full square curve, horizontal line and identity line on separate sheets. Cut away the inputs their conditions reject. Place the remaining pieces on one coordinate plane.

As boundary ownership

At x = 1 in the given function, (1, 1) belongs and (1, 3) does not. At x = 2, (2, 3) belongs and (2, 2) does not. The filled point gives the function value.

As a picture convention

A filled endpoint is present, and a hollow endpoint is absent. A piecewise graph can show several endpoint markers at one input, but the vertical line test counts only the included points.

1213
Filled and hollow endpoint dots distinguish included graph points from boundary locations that are absent.
As two separate unions

The given function's input pieces fill the whole real number line. Its square branch alone already reaches every nonnegative output. Other pieces can change which input gives a height without adding new heights to the range.

.1Draw the quadratic branch

The first branch uses the familiar square curve. Its condition keeps all inputs at most 1, including negative inputs far to the left. That left arm keeps rising, so this one branch reaches output heights much larger than its right endpoint's height.

  • Formula: x2 for x ≤ 1.
  • Closed endpoint: (1, 1).
  • Included vertex: (0, 0).
  • Branch domain: (−∞, 1]; branch range: [0, ∞).
1213
This is the completed three-piece graph. In this part, inspect only the quadratic branch on x ≤ 1, including (1, 1) and the vertex (0, 0). The other two branches belong to the whole function. For the whole graph, the included points at inputs 1 and 2 are (1, 1) and (2, 3); the other boundary circles are open.
Reminder
  • Substitution. If f(x) = x2 on the selected branch, f(1) means replace x by 1 and compute 12 = 1.
  • Equality at a boundary. 1 < x ≤ 2 includes 2, while x > 2 does not.
  • Principal square root. If y ≥ 0, y is nonnegative and (−y)2 = y.
The same idea, five ways
Say it

Say keep the square curve through input one and all inputs to its left.

Write it

The quadratic branch includes its boundary and reaches every nonnegative height.

In math
  • f(x) = x2 if x ≤ 1
  • Branch domain: (−∞, 1]
  • Branch range: [0, ∞)
  • Graph words: closed (1, 1), vertex (0, 0), left arm continues
Like

Cut away only the forbidden input side of a drawn square curve.

See it
1213
This is the completed three-piece graph. In this part, inspect only the quadratic branch on x ≤ 1, including (1, 1) and the vertex (0, 0). The other two branches belong to the whole function. For the whole graph, the included points at inputs 1 and 2 are (1, 1) and (2, 3); the other boundary circles are open.
Worked exampleDraw the first branch of the given function

Graph only the branch f(x) = x2 for x ≤ 1.

input xoutput x²−24−110011↓ evaluate: input given, read the output below it
The four input columns give the points for the square branch.
1213
This is the completed three-piece graph. In this part, inspect only the quadratic branch on x ≤ 1, including (1, 1) and the vertex (0, 0). The other two branches belong to the whole function. For the whole graph, the included points at inputs 1 and 2 are (1, 1) and (2, 3); the other boundary circles are open.
1(−∞, 1]
Keep the square curve only on this input interval.
  1. We need the included graph points, keeping only the assigned input interval.State what is being found before choosing the calculation.
  2. Mark the boundary x = 1 and choose sample inputs −2, −1, 0 and 1.All these inputs satisfy this branch's condition.
  3. Read the column under −2: (−2)2 = 4. Under −1, (−1)2 = 1. Under 0, 02 = 0. Under 1, 12 = 1.Squaring each selected input supplies points on the quadratic shape.
  4. Draw the U-shaped curve through these points, keeping only x ≤ 1.The formula is assigned to this interval alone.
  5. Place a closed dot at (1, 1) and extend the left side upward with an arrow.Equality includes x = 1, and there is no lower input bound.
  6. This branch has domain (−∞, 1] and range [0, ∞).The vertex reaches zero, and arbitrarily negative inputs have arbitrarily large squares.
Answer
  • Plot (−2, 4), (−1, 1), (0, 0) and the closed point (1, 1).
  • Keep the curve only for x ≤ 1.
  • Branch domain: (−∞, 1].
  • Branch range: [0, ∞).
Check For any desired y ≥ 0, x = −y is at most zero, hence allowed, and x2 = y. This proves every claimed height occurs.
Counterexamples: what it is not, and the tempting wrong moves
✗ Not this: The branch x2 for x ≤ 1 has no outputs above 1.
The restriction limits inputs, and negative inputs can have large squares.
✓ Instead: Input −3 is allowed and gives 9. This branch has range [0, ∞).
Tips and tricks
  • Use a negative sample input to remember the rising left arm.
.2Draw the constant branch

The middle branch is a horizontal shelf at height 3. It begins after input 1 and includes input 2. Every position on that shelf has the same output. The endpoints have different inclusion rules even though the shelf is flat.

  • Formula: 3 for 1 < x ≤ 2.
  • Open endpoint: (1, 3); closed endpoint: (2, 3).
  • Branch domain: (1, 2]; branch range: {3}.
12
This is the middle branch's input interval, with 1 excluded and 2 included.
Reminder
  • Substitution. If f(x) = x2 on the selected branch, f(1) means replace x by 1 and compute 12 = 1.
  • Equality at a boundary. 1 < x ≤ 2 includes 2, while x > 2 does not.
  • Principal square root. If y ≥ 0, y is nonnegative and (−y)2 = y.
The same idea, five ways
Say it

Say a shelf after input one through input two.

Write it

The constant branch excludes its left boundary and includes its right boundary.

In math
  • f(x) = 3 if 1 < x ≤ 2
  • Branch domain: (1, 2]
  • Branch range: {3} = [3, 3]
  • Graph words: open (1, 3), closed (2, 3)
Like

A horizontal shelf keeps the same height across its allowed span.

See it
12
This is the middle branch's input interval, with 1 excluded and 2 included.
Worked exampleDraw the middle branch of the given function

Graph only f(x) = 3 for 1 < x ≤ 2.

1213
The included points at inputs 1 and 2 are (1, 1) and (2, 3); the other boundary circles are open.
12
This is the middle branch's input interval, with 1 excluded and 2 included.
  1. We need the included graph points, keeping only the assigned input interval.State what is being found before choosing the calculation.
  2. Mark the interval from 1 to 2.The condition restricts this branch to those input positions.
  3. Draw a horizontal segment at y = 3.The output stays 3 for every input in this interval.
  4. Use an open dot at (1, 3) and a closed dot at (2, 3).The left comparison is strict and the right comparison includes equality.
  5. The branch domain is (1, 2] and range is {3}.Many allowed inputs produce the single output 3.
Answer
  • Draw a horizontal segment at height 3.
  • Open point: (1, 3).
  • Closed point: (2, 3).
  • Branch domain: (1, 2].
  • Branch range: {3}, also [3, 3].
Check The allowed input 1.5 gives 3, while this branch does not assign anything to x = 1.
Counterexamples: what it is not, and the tempting wrong moves
✗ Not this: Include (1, 3) on the middle shelf.
The condition is 1 < x ≤ 2, so 1 is excluded from this branch.
✓ Instead: Use open (1, 3) and closed (2, 3).
Tips and tricks
  • Mark each endpoint from its own comparison sign.
.3Draw the identity branch

The last branch follows the slanted line where output equals input. It starts strictly after 2, so the point (2, 2) is hollow. The whole function still has a value at input 2 because the middle branch supplies it at height 3.

  • Formula: x for x > 2.
  • Open boundary point: (2, 2).
  • Sample included points: (3, 3) and (4, 4).
  • Branch domain and branch range: (2, ∞).
Open boundary: (2, 2)
Included points: (3, 3), (4, 4)
Continue upward and rightward
The last branch excludes input 2 without removing input 2 from the whole function's domain.
Reminder
  • Substitution. If f(x) = x2 on the selected branch, f(1) means replace x by 1 and compute 12 = 1.
  • Equality at a boundary. 1 < x ≤ 2 includes 2, while x > 2 does not.
  • Principal square root. If y ≥ 0, y is nonnegative and (−y)2 = y.
The same idea, five ways
Say it

Say copy each input strictly above two.

Write it

The last branch is the identity line only to the right of its excluded boundary.

In math
  • f(x) = x if x > 2
  • Branch domain and range: (2, ∞)
  • Graph words: open (2, 2), ray through (3, 3) and (4, 4)
Like

A diagonal path keeps the horizontal position and vertical height equal.

See it
Open boundary: (2, 2)
Included points: (3, 3), (4, 4)
Continue upward and rightward
The last branch excludes input 2 without removing input 2 from the whole function's domain.
Worked exampleDraw the final branch of the given function

Graph only f(x) = x for x > 2.

1213
The included points at inputs 1 and 2 are (1, 1) and (2, 3); the other boundary circles are open.
Open boundary: (2, 2)
Included points: (3, 3), (4, 4)
Continue upward and rightward
The last branch excludes input 2 without removing input 2 from the whole function's domain.
  1. We need the included graph points, keeping only the assigned input interval.State what is being found before choosing the calculation.
  2. Compute the boundary position (2, 2), but leave it open.The formula would give 2 there, but the condition excludes that input from this branch.
  3. Plot (3, 3) and (4, 4).Both inputs are above 2, and the identity rule keeps their values.
  4. Draw a straight ray through the included points and continue upward to the right.The identity graph is a line and has no upper input bound.
  5. Write (2, ∞) for both this branch's domain and range.The included inputs and identical outputs are strictly greater than 2.
Answer
  • Open point: (2, 2).
  • Draw the ray through (3, 3) and (4, 4), continuing rightward.
  • Branch domain: (2, ∞).
  • Branch range: (2, ∞).
Check The output 2 is not supplied by this branch, but every output greater than 2 comes from the input with the same value.
Counterexamples: what it is not, and the tempting wrong moves
✗ Not this: The last branch supplies f(2) = 2.
Its condition is x > 2, so its point (2, 2) is absent.
✓ Instead: The middle branch supplies f(2) = 3.
Tips and tricks
  • A branch exclusion does not remove an input assigned by another branch.
Strategy: step by step
  1. 1. Mark every boundary input on one common x-axis.
  2. 2. Identify each formula's known shape and calculate at least two useful points, or include a turning point for a curve.
  3. 3. Keep only the portion satisfying that branch's condition.
  4. 4. Calculate the boundary height and make its dot open or closed according to that branch's inequality.
  5. 5. Combine all allowed portions without inventing connecting segments across jumps or gaps.
  6. 6. Check the vertical line test at every boundary, then collect the domain and range shadows.
Strategy
Build a piecewise graph
1
Does the branch include its boundary?
YesDraw a closed dot at the calculated boundary point.
NoDraw an open dot there.
↓
2
Is there a jump or gap?
YesLeave it unconnected.
NoKeep only the allowed curve or line portions.
↓
3
Does a vertical line hit two different included points?
YesThe plotted rule fails to be a function there; check the conditions.
NoRead and combine the branch shadows.
  1. 1. Mark every boundary input on one common x-axis.
  2. 2. Identify each formula's known shape and calculate at least two useful points, or include a turning point for a curve.
  3. 3. Keep only the portion satisfying that branch's condition.
  4. 4. Calculate the boundary height and make its dot open or closed according to that branch's inequality.
  5. 5. Combine all allowed portions without inventing connecting segments across jumps or gaps.
  6. 6. Check the vertical line test at every boundary, then collect the domain and range shadows.
Worked examplegraph and read all three pieces

Let f(x) = x2 if x ≤ 1, f(x) = 3 if 1 < x ≤ 2, and f(x) = x if x > 2. Graph it, find f(1), f(1.5), f(2) and f(4), and state domain and range.

1213
The included points at inputs 1 and 2 are (1, 1) and (2, 3); the other boundary circles are open.
  1. We need every allowed input and every output the rule actually reaches.State what is being found before choosing the calculation.
  2. Draw y = x2 only for x ≤ 1, with a closed point at (1, 1).The first condition includes its boundary; the square curve has its lowest point at (0, 0).
  3. Draw y = 3 on 1 < x ≤ 2, with an open point at (1, 3) and a closed point at (2, 3).This condition excludes its left endpoint and includes its right endpoint.
  4. Draw y = x only for x > 2, beginning with an open point at (2, 2).The third condition excludes 2, so its line does not assign an output there.
  5. At x = 1, choose the first branch and calculate 12 = 1.The ≤ 1 condition owns this boundary.
  6. At x = 1.5, choose the middle branch and get 3.1 < 1.5 ≤ 2.
  7. At x = 2, also choose the middle branch and get 3.The middle condition includes equality at 2; the final branch does not.
  8. At x = 4, choose the last branch and get 4.4 satisfies x > 2.
  9. Take the input union (−∞, 1] ∪ (1, 2] ∪ (2, ∞) = (−∞, ∞).Every real input belongs to one of these three intervals, with no gap.
  10. The first branch already reaches every y ≥ 0, and neither other branch goes below zero.For any y ≥ 0 the allowed input −y supplies that output through the first branch.
  11. Write range [0, ∞).Union with {3} and (2, ∞) adds no new values beyond the first branch's range.
Answer
  • f(1) = 1.
  • f(1.5) = 3.
  • f(2) = 3.
  • f(4) = 4.
  • Domain: (−∞, ∞).
  • Range: [0, ∞).
Check At x = 1 the only included boundary point is (1, 1), and at x = 2 it is (2, 3). The open points are absent, so a vertical line meets exactly one included point at either boundary. Also f(−3) = 9 confirms that the first branch's output heights continue above the constant piece.
Ladder: from easy to exam-hard. Press Try it first on any rung to hide its steps and use them as hints.
Rung 1Graphing ladder 1: two pieces that meet

Graph F(x) = x for x < 0 and F(x) = 2x for x ≥ 0. State domain and range.

−6−4−2246−8−6−4−224681012
This is the full line y = x; use the next picture to keep only the branch’s allowed inputs.
0(−∞, 0)
Keep only x < 0 from y = x.
−6−4−2246−8−6−4−224681012
This is the full line y = 2x; use the next picture to keep only the branch’s allowed inputs.
0[0, ∞)
Keep only x ≥ 0 from y = 2x.
  1. We need every allowed input and every output the rule actually reaches.State what is being found before choosing the calculation.
  2. Draw the line y = x only left of 0 with an open point at (0, 0).The first branch excludes its boundary and gives negative outputs for negative inputs.
  3. Draw the line y = 2x on and right of 0 with a closed point at (0, 0), passing through (1, 2).The second branch includes the boundary and has twice the input as its output.
  4. Keep the included point at (0, 0) where the branches meet.An open marker from the first piece does not remove a point included by the second piece.
  5. Take the domain union (−∞, 0) ∪ [0, ∞).All negative and nonnegative inputs are covered.
  6. Take the range union (−∞, 0) ∪ [0, ∞).The first piece reaches every negative output; the second reaches every nonnegative output.
Answer
  • Domain: (−∞, ∞).
  • Range: (−∞, ∞).
  • The graph has an included point at (0, 0).
Check For a negative output y choose x = y in the first branch. For a nonnegative output y choose x = y2 in the second branch.
Rung 2Graphing ladder 2: a jump creates a missing output interval

Graph G(x) = x − 2 for x < 4 and G(x) = x + 3 for x ≥ 4. Find domain and range.

−6−4−2246−8−6−4−224681012
This is the full line y = x − 2; use the next picture to keep only the branch’s allowed inputs.
4(−∞, 4)
Keep only x < 4 from y = x − 2; (4, 2) is open.
−6−4−2246−8−6−4−224681012
This is the full line y = x + 3; use the next picture to keep only the branch’s allowed inputs.
4[4, ∞)
Keep only x ≥ 4 from y = x + 3; (4, 7) is closed.
27(−∞, 2) ∪ [7, ∞)
Range: (−∞, 2) ∪ [7, ∞). The endpoint symbols record which limits belong.
  1. We need every allowed input and every output the rule actually reaches.State what is being found before choosing the calculation.
  2. Draw y = x − 2 left of 4, ending at the open point (4, 2).Inputs below 4 use the first branch. At 4 it would give 4 − 2 = 2, but 4 is not below 4, so that point is hollow and these outputs stay strictly below 2.
  3. Draw y = x + 3 on and right of 4, starting at the closed point (4, 7) and passing through (5, 8).The second branch includes 4, where 4 + 3 = 7, and it produces outputs at least 7.
  4. The input intervals join to all real numbers.Every real input is either below 4 or at least 4.
  5. The output intervals remain (−∞, 2) and [7, ∞).No included point reaches a height from 2 up to but not including 7.
  6. Join the output intervals with ∪.A union preserves the missing heights rather than filling them.
Answer
  • Domain: (−∞, ∞).
  • Range: (−∞, 2) ∪ [7, ∞).
  • G(4) = 7.
Check The output 5 cannot occur: x − 2 = 5 needs x = 7, which is not below 4, and x + 3 = 5 needs x = 2, which is not at least 4. A vertical line at x = 4 meets only the included point (4, 7).
Rung 3graph and read all three pieces

Let f(x) = x2 if x ≤ 1, f(x) = 3 if 1 < x ≤ 2, and f(x) = x if x > 2. Graph it, find f(1), f(1.5), f(2) and f(4), and state domain and range.

1213
The included points at inputs 1 and 2 are (1, 1) and (2, 3); the other boundary circles are open.
  1. We need every allowed input and every output the rule actually reaches.State what is being found before choosing the calculation.
  2. Draw y = x2 only for x ≤ 1, with a closed point at (1, 1).The first condition includes its boundary; the square curve has its lowest point at (0, 0).
  3. Draw y = 3 on 1 < x ≤ 2, with an open point at (1, 3) and a closed point at (2, 3).This condition excludes its left endpoint and includes its right endpoint.
  4. Draw y = x only for x > 2, beginning with an open point at (2, 2).The third condition excludes 2, so its line does not assign an output there.
  5. At x = 1, choose the first branch and calculate 12 = 1.The ≤ 1 condition owns this boundary.
  6. At x = 1.5, choose the middle branch and get 3.1 < 1.5 ≤ 2.
  7. At x = 2, also choose the middle branch and get 3.The middle condition includes equality at 2; the final branch does not.
  8. At x = 4, choose the last branch and get 4.4 satisfies x > 2.
  9. Take the input union (−∞, 1] ∪ (1, 2] ∪ (2, ∞) = (−∞, ∞).Every real input belongs to one of these three intervals, with no gap.
  10. The first branch already reaches every y ≥ 0, and neither other branch goes below zero.For any y ≥ 0 the allowed input −y supplies that output through the first branch.
  11. Write range [0, ∞).Union with {3} and (2, ∞) adds no new values beyond the first branch's range.
Answer
  • f(1) = 1.
  • f(1.5) = 3.
  • f(2) = 3.
  • f(4) = 4.
  • Domain: (−∞, ∞).
  • Range: [0, ∞).
Check At x = 1 the only included boundary point is (1, 1), and at x = 2 it is (2, 3). The open points are absent, so a vertical line meets exactly one included point at either boundary. Also f(−3) = 9 confirms that the first branch's output heights continue above the constant piece.
Rung 4Graphing ladder 4: missing inputs and missing outputs

Let H(x) = x if x < −1 and H(x) = x + 2 if x ≥ 2. Graph it and state its domain and range.

−6−4−2246−8−6−4−224681012
This is the full line y = x; use the next picture to keep only the branch’s allowed inputs.
−1(−∞, −1)
Keep only x < −1 from y = x.
−6−4−2246−8−6−4−224681012
This is the full line y = x + 2; use the next picture to keep only the branch’s allowed inputs.
2[2, ∞)
Keep only x ≥ 2 from y = x + 2.
−12(−∞, −1) ∪ [2, ∞)
Domain: (−∞, −1) ∪ [2, ∞). The endpoint symbols record which limits belong.
−14(−∞, −1) ∪ [4, ∞)
Range: (−∞, −1) ∪ [4, ∞). The endpoint symbols record which limits belong.
  1. We need every allowed input and every output the rule actually reaches.State what is being found before choosing the calculation.
  2. Draw y = x for x < −1, ending with an open point at (−1, −1).The first branch excludes its right boundary and extends downward to the left.
  3. Leave all inputs from −1 through values below 2 blank.Neither condition assigns an output to those inputs.
  4. Draw y = x + 2 for x ≥ 2, starting with a closed point at (2, 4) and passing through (3, 5).The second condition includes 2 and gives output 2 + 2 = 4 there.
  5. Write domain (−∞, −1) ∪ [2, ∞).These are exactly the two allowed input intervals.
  6. Write range (−∞, −1) ∪ [4, ∞).The first line reaches every height below −1; the second reaches every height at least 4.
Answer
  • Domain: (−∞, −1) ∪ [2, ∞).
  • Range: (−∞, −1) ∪ [4, ∞).
  • H(0) is undefined.
Check For y < −1, choose x = y in the first branch. For y ≥ 4, choose x = y − 2 ≥ 2 in the second. The outputs in the claimed range all have an allowed input.
Rung 5Graph a constant and a square-root branch

Let Q(x) = 5 if x < −4 and Q(x) = x+4 if x ≥ −4. Graph the two assigned pieces and find domain and range. You are drawing each shape only for its own input condition, then collecting the whole graph’s two shadows.

−8−6−4−22246
This is the full constant line; keep only its inputs x < −4, leaving (−4, 5) open.
−4(−∞, −4)
The constant branch uses only these inputs.
−6−4−2246824rangeclosed start(0, 2)(5, 3)
This root curve already has exactly its assigned inputs x ≥ −4 and includes its start.
  1. For x < −4, draw a horizontal ray at height 5, with an open point at (−4, 5) and continuation to the left.The constant rule gives one height on its assigned inputs, and the strict condition excludes the boundary.
  2. For x ≥ −4, draw the root curve beginning at the closed point (−4, 0). At x = 0 it passes through (0, 2), and at x = 5 it passes through (5, 3).Substitution gives 0 = 0, 4 = 2, and 9 = 3. The second condition includes the starting input and its root is real for every assigned input.
  3. Take the input union (−∞, −4) ∪ [−4, ∞) = (−∞, ∞).Every input below the boundary uses the constant, and every input at or above it uses the root, so none is missing.
  4. The constant branch gives {5}. The root branch gives [0, ∞), because any target y ≥ 0 comes from x = y2 − 4 ≥ −4.The nonnegative root outputs are all attained by the constructed input.
  5. The full output union is {5} ∪ [0, ∞) = [0, ∞).Output 5 already lies in the root range, so including the constant branch adds no new height.
Answer
  • Domain: (−∞, ∞).
  • Range: [0, ∞).
  • Q(−4) = 0.
Check At the boundary, the point (−4, 5) is absent and (−4, 0) is included, so the vertical line there has exactly one included crossing. Output 5 is reached at negative inputs and also at x = 21 because 25 = 5.
Rung 6Three shapes with two omitted boundary inputs

Let P(x) = x3 if x < −3, P(x) = −7 if −3 < x < 9, and P(x) = x−5 if x > 9. Graph the pieces and find domain and range. You are retaining the branch shapes only on the stated intervals, including any missing inputs or isolated output heights.

−6−4−2−144−128−112−96−80−64−48−32−16
This is the full cube shape; keep only x < −3 and leave its boundary location (−3, −27) open.
−3(−∞, −3)
The cube branch has exactly these inputs.
−4−2246810−10−8−6−4−2
This is the full constant line; keep only −3 < x < 9 with both endpoints open.
−39(−3, 9)
The middle branch includes every input strictly between the two omitted boundaries.
4681012141624
This is the full square-root shape; keep only x > 9, leaving (9, 2) open.
9(9, ∞)
The root branch uses these inputs rather than all inputs allowed by its full shape.
−27−72(−∞, −27) ∪ [−7, −7] ∪ (2, ∞)
The output shadow has two unbounded pieces and the one included height −7.
  1. Draw the cube curve only for x < −3. At its right boundary the formula would give (−3)3 = −27, so place an open point at (−3, −27).The strict condition excludes −3. Every earlier input gives a cube below −27.
  2. Draw a horizontal segment at height −7 only for −3 < x < 9, with both (−3, −7) and (9, −7) open.Both comparisons are strict, although every interior input supplies the actual output −7.
  3. For x > 9, the root curve’s boundary location is (9, 2), because 9−5 = 4 = 2. Leave that point open, and draw the curve through (14, 3), continuing rightward.Only inputs above 9 belong to this branch; they make the root inside greater than 4, so their root outputs are strictly greater than 2.
  4. Keep both missing input values and write (−∞, −3) ∪ (−3, 9) ∪ (9, ∞).No condition includes −3 or 9; each other real input belongs to exactly one branch.
  5. The cube branch reaches exactly (−∞, −27): for any y < −27, the input y3 is below −3 and cubes to y. The middle branch reaches the single value −7.Cubing preserves input order, and the constant branch has only one output despite its many inputs.
  6. The root branch reaches (2, ∞): for any target y > 2, choose x = y2 + 5 > 9; then x−5 = y.The target is positive, so its square exceeds 4 and the principal root returns y. This proves every claimed root height is attained.
  7. Combine the three output sets as (−∞, −27) ∪ [−7, −7] ∪ (2, ∞).The isolated height −7 belongs. A one-member set can be written [−7, −7], and union must preserve all missing heights around it.
Answer
  • Domain: (−∞, −3) ∪ (−3, 9) ∪ (9, ∞).
  • Range: (−∞, −27) ∪ [−7, −7] ∪ (2, ∞).
  • P(−3) and P(9) are undefined.
Check Input −4 gives −64, input 0 gives −7, and input 14 gives 3. Each value belongs to its listed range piece. No included point reaches −27 or 2: their only matching branch boundary inputs are excluded.
Counterexamples: what it is not, and the tempting wrong moves
✗ Not this: Connect (1, 1) to (1, 3) with a vertical line segment.
That would give several included output heights for the one input x = 1.
✓ Instead: Keep (1, 1) closed and (1, 3) open, without connecting the jump.
✗ Not this: At x = 2, take the identity formula and output 2.
The identity branch requires x > 2. The middle branch owns x = 2.
✓ Instead: f(2) = 3.
Tips and tricks
  • List each branch's domain and range separately before taking the two unions.
  • Count only filled points in a vertical line test at a boundary.
  • Keep jumps and missing intervals visible. Do not draw extra connecting segments.
Trap. Joining the endpoint (1, 1) to the hollow endpoint (1, 3) with a vertical segment. That segment would create many outputs for x = 1. A jump stays a jump; it is not filled in.