Trapezoidal Rule
Mathematics · FE Reference Handbook section
Core formulas for this FE topic
Definitions, applicability, units, assumptions and worked examples for each relation.
Worked exam-style examples
The four ways this section is written on the real exam — thoughts first, then equations, then substitution.
An engineer applies the trapezoidal rule to approximate the area under a velocity curve. Given step size (h) = 1.4000; f(x0) (f0) = 7.4000; f(x1) (f1) = 5.7000; f(x2) (f2) = 5.9000, determine the approx. integral (I).
Given
Find
approx. integral (I)
Start with the thinking
- The governing relation printed in this handbook section is Trapezoidal rule for numerical integration.
- Everything except I is given, so isolate I symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The trapezoidal rule approximates a definite integral by summing trapezoid areas between panel points.
Figure 1 — schematic for Trapezoidal rule for numerical integration — solve for approx. integral — Trapezoidal Rule
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for I:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning I = 17.2900 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 34.5800 — kept a factor of two that cancels in the correct rearrangement.
- 8.6450 — dropped that same factor in the other direction.
- 19.0190 — rounded an intermediate value before the final step.
Reference: FE Handbook — Trapezoidal Rule
A student uses the trapezoidal rule to estimate an integral from tabulated data. Given f(x0) (f0) = 4.8000; f(x1) (f1) = 1.0000; f(x2) (f2) = 3.0000; approx. integral (I) = 100.8, determine the step size (h).
Given
Find
step size (h)
Start with the thinking
- The governing relation printed in this handbook section is Trapezoidal rule for numerical integration.
- Everything except h is given, so isolate h symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The trapezoidal rule approximates a definite integral by summing trapezoid areas between panel points.
Figure 2 — schematic for Trapezoidal rule for numerical integration — solve for step size — Trapezoidal Rule (2)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for h:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning h = 20.5714 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 41.1429 — kept a factor of two that cancels in the correct rearrangement.
- 10.2857 — dropped that same factor in the other direction.
- 22.6286 — rounded an intermediate value before the final step.
Reference: FE Handbook — Trapezoidal Rule
The trapezoidal rule is used to approximate the flow volume from measured readings. Given step size (h) = 2.8000; f(x0) (f0) = 4.4000; f(x2) (f2) = 2.0000; approx. integral (I) = 47.7300, determine the f(x1) (f1).
Given
Find
f(x1) (f1)
Start with the thinking
- The governing relation printed in this handbook section is Trapezoidal rule for numerical integration.
- Everything except f1 is given, so isolate f1 symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The trapezoidal rule approximates a definite integral by summing trapezoid areas between panel points.
Figure 3 — schematic for Trapezoidal rule for numerical integration — solve for f(x1) — Trapezoidal Rule (3)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for f1:
Step 3 — List the givens: step size (h) = 2.8000, f(x0) (f0) = 4.4000, f(x2) (f2) = 2.0000, approx. integral (I) = 47.7300.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning f1 = 13.8464 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 27.6929 — kept a factor of two that cancels in the correct rearrangement.
- 6.9232 — dropped that same factor in the other direction.
- 15.2311 — rounded an intermediate value before the final step.
Reference: FE Handbook — Trapezoidal Rule
An engineer applies the trapezoidal rule to approximate the area under a velocity curve. Given step size (h) = 1.5000; f(x0) (f0) = 3.9000; f(x1) (f1) = 4.9000; f(x2) (f2) = 3.2000, determine the approx. integral (I).
Given
Find
approx. integral (I)
Start with the thinking
- The governing relation printed in this handbook section is Trapezoidal rule for numerical integration.
- Everything except I is given, so isolate I symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The trapezoidal rule approximates a definite integral by summing trapezoid areas between panel points.
Figure 4 — schematic for Trapezoidal rule for numerical integration — solve for approx. integral (case 2) — Trapezoidal Rule (4)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for I:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning I = 12.6750 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 25.3500 — kept a factor of two that cancels in the correct rearrangement.
- 6.3375 — dropped that same factor in the other direction.
- 13.9425 — rounded an intermediate value before the final step.
Reference: FE Handbook — Trapezoidal Rule
A student uses the trapezoidal rule to estimate an integral from tabulated data. Given f(x0) (f0) = 8.6000; f(x1) (f1) = 5.3000; f(x2) (f2) = 7.4000; approx. integral (I) = 53.3900, determine the step size (h).
Given
Find
step size (h)
Start with the thinking
- The governing relation printed in this handbook section is Trapezoidal rule for numerical integration.
- Everything except h is given, so isolate h symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The trapezoidal rule approximates a definite integral by summing trapezoid areas between panel points.
Figure 5 — schematic for Trapezoidal rule for numerical integration — solve for step size (case 2) — Trapezoidal Rule (5)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for h:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning h = 4.0143 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 8.0286 — kept a factor of two that cancels in the correct rearrangement.
- 2.0071 — dropped that same factor in the other direction.
- 4.4157 — rounded an intermediate value before the final step.
Reference: FE Handbook — Trapezoidal Rule
The trapezoidal rule is used to approximate the flow volume from measured readings. Given step size (h) = 1.5000; f(x0) (f0) = 5.6000; f(x2) (f2) = 2.7000; approx. integral (I) = 84.2500, determine the f(x1) (f1).
Given
Find
f(x1) (f1)
Start with the thinking
- The governing relation printed in this handbook section is Trapezoidal rule for numerical integration.
- Everything except f1 is given, so isolate f1 symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The trapezoidal rule approximates a definite integral by summing trapezoid areas between panel points.
Figure 6 — schematic for Trapezoidal rule for numerical integration — solve for f(x1) (case 2) — Trapezoidal Rule (6)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for f1:
Step 3 — List the givens: step size (h) = 1.5000, f(x0) (f0) = 5.6000, f(x2) (f2) = 2.7000, approx. integral (I) = 84.2500.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning f1 = 52.0167 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 104.0 — kept a factor of two that cancels in the correct rearrangement.
- 26.0083 — dropped that same factor in the other direction.
- 57.2183 — rounded an intermediate value before the final step.
Reference: FE Handbook — Trapezoidal Rule
An engineer applies the trapezoidal rule to approximate the area under a velocity curve. Given step size (h) = 0.8000; f(x0) (f0) = 5.7000; f(x1) (f1) = 1.5000; f(x2) (f2) = 4.4000, determine the approx. integral (I).
Given
Find
approx. integral (I)
Start with the thinking
- The governing relation printed in this handbook section is Trapezoidal rule for numerical integration.
- Everything except I is given, so isolate I symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The trapezoidal rule approximates a definite integral by summing trapezoid areas between panel points.
Figure 7 — schematic for Trapezoidal rule for numerical integration — solve for approx. integral (case 3) — Trapezoidal Rule (7)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for I:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning I = 5.2400 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 10.4800 — kept a factor of two that cancels in the correct rearrangement.
- 2.6200 — dropped that same factor in the other direction.
- 5.7640 — rounded an intermediate value before the final step.
Reference: FE Handbook — Trapezoidal Rule
A student uses the trapezoidal rule to estimate an integral from tabulated data. Given f(x0) (f0) = 6.8000; f(x1) (f1) = 4.1000; f(x2) (f2) = 5.9000; approx. integral (I) = 82.6200, determine the step size (h).
Given
Find
step size (h)
Start with the thinking
- The governing relation printed in this handbook section is Trapezoidal rule for numerical integration.
- Everything except h is given, so isolate h symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The trapezoidal rule approximates a definite integral by summing trapezoid areas between panel points.
Figure 8 — schematic for Trapezoidal rule for numerical integration — solve for step size (case 3) — Trapezoidal Rule (8)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for h:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning h = 7.9062 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 15.8124 — kept a factor of two that cancels in the correct rearrangement.
- 3.9531 — dropped that same factor in the other direction.
- 8.6968 — rounded an intermediate value before the final step.
Reference: FE Handbook — Trapezoidal Rule
The trapezoidal rule is used to approximate the flow volume from measured readings. Given step size (h) = 2.4000; f(x0) (f0) = 7.1000; f(x2) (f2) = 9.7000; approx. integral (I) = 59.9200, determine the f(x1) (f1).
Given
Find
f(x1) (f1)
Start with the thinking
- The governing relation printed in this handbook section is Trapezoidal rule for numerical integration.
- Everything except f1 is given, so isolate f1 symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The trapezoidal rule approximates a definite integral by summing trapezoid areas between panel points.
Figure 9 — schematic for Trapezoidal rule for numerical integration — solve for f(x1) (case 3) — Trapezoidal Rule (9)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for f1:
Step 3 — List the givens: step size (h) = 2.4000, f(x0) (f0) = 7.1000, f(x2) (f2) = 9.7000, approx. integral (I) = 59.9200.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning f1 = 16.5667 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 33.1333 — kept a factor of two that cancels in the correct rearrangement.
- 8.2833 — dropped that same factor in the other direction.
- 18.2233 — rounded an intermediate value before the final step.
Reference: FE Handbook — Trapezoidal Rule
An engineer applies the trapezoidal rule to approximate the area under a velocity curve. Given step size (h) = 1.8000; f(x0) (f0) = 6.2000; f(x1) (f1) = 1.2000; f(x2) (f2) = 7.7000, determine the approx. integral (I).
Given
Find
approx. integral (I)
Start with the thinking
- The governing relation printed in this handbook section is Trapezoidal rule for numerical integration.
- Everything except I is given, so isolate I symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The trapezoidal rule approximates a definite integral by summing trapezoid areas between panel points.
Figure 10 — schematic for Trapezoidal rule for numerical integration — solve for approx. integral (case 4) — Trapezoidal Rule (10)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for I:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning I = 14.6700 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 29.3400 — kept a factor of two that cancels in the correct rearrangement.
- 7.3350 — dropped that same factor in the other direction.
- 16.1370 — rounded an intermediate value before the final step.
Reference: FE Handbook — Trapezoidal Rule