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Product of Inertia

Statics · FE Reference Handbook section

Statics
4 formulas
10 exam-style examples
~53 min
All Statics lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • The parallel-axis theorem also applies:

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.

Example 1
Product of inertia (rectangle) — solve for product of inertia — Product of Inertia

An unsymmetric angle section requires the product of inertia for principal axis analysis. Given area (A) = 53.5000 in^2; centroidal x offset (x_bar) = -1.5000 in; centroidal y offset (y_bar) = -6.0000 in, determine the product of inertia (I_xy) in in^4.

Given

  • area(A)=53.5000in2area (A) = 53.5000 in^2
  • centroidalxoffset(xbar)=−1.5000incentroidal x offset (x_bar) = -1.5000 in
  • centroidalyoffset(ybar)=−6.0000incentroidal y offset (y_bar) = -6.0000 in

Find

product of inertia (I_xy), in in^4

Start with the thinking

  • The governing relation printed in this handbook section is Product of inertia (rectangle).
  • Everything except I_xy is given, so isolate I_xy 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 product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Section for product of inertiacentroidal axisb = 4h = 6

Figure 1 — schematic for Product of inertia (rectangle) — solve for product of inertia — Product of Inertia

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  2. Step 2 — Rearrange symbolically for I_xy:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  3. Step 3 — List the givens: area (A) = 53.5000 in^2, centroidal x offset (x_bar) = -1.5000 in, centroidal y offset (y_bar) = -6.0000 in.

  4. Step 4 — Substitute the given values:

    Ixy=53.5000xˉyˉI_{xy} = 53.5000 \bar{x} \bar{y}
  5. Step 5 — Evaluate:

    I_{xy} = 481.5\ \text{in^4}
  6. Step 6 — Check: returning I_xy = 481.5 in^4 to

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}

    reproduces the given quantities, and both sides carry the same units.

Answer:
I_{xy} = 481.5\ \text{in^4}

Why the other options are there

  • 963.0 — kept a factor of two that cancels in the correct rearrangement.
  • 240.8 — dropped that same factor in the other direction.
  • 529.7 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Product of Inertia

Example 2
Product of inertia (rectangle) — solve for area — Product of Inertia (2)

A composite area's product of inertia about its centroid is needed before rotating axes. Given centroidal x offset (x_bar) = -5.1000 in; centroidal y offset (y_bar) = 5.0000 in; product of inertia (I_xy) = 97.0000 in^4, determine the area (A) in in^2.

Given

  • centroidalxoffset(xbar)=−5.1000incentroidal x offset (x_bar) = -5.1000 in
  • centroidalyoffset(ybar)=5.0000incentroidal y offset (y_bar) = 5.0000 in
  • productofinertia(Ixy)=97.0000in4product of inertia (I_xy) = 97.0000 in^4

Find

area (A), in in^2

Start with the thinking

  • The governing relation printed in this handbook section is Product of inertia (rectangle).
  • Everything except A is given, so isolate A 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 product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Section for product of inertiacentroidal axisb = 4h = 6

Figure 2 — schematic for Product of inertia (rectangle) — solve for area — Product of Inertia (2)

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  2. Step 2 — Rearrange symbolically for A:

    A=Ixyxˉ yˉA = \dfrac{I_{xy}}{\bar{x}\,\bar{y}}
  3. Step 3 — List the givens: centroidal x offset (x_bar) = -5.1000 in, centroidal y offset (y_bar) = 5.0000 in, product of inertia (I_xy) = 97.0000 in^4.

  4. Step 4 — Substitute the given values:

    A=97.0000xˉ yˉA = \dfrac{97.0000}{\bar{x}\,\bar{y}}
  5. Step 5 — Evaluate:

    A = -3.8039\ \text{in^2}
  6. Step 6 — Check: returning A = -3.8039 in^2 to

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}

    reproduces the given quantities, and both sides carry the same units.

Answer:
A = -3.8039\ \text{in^2}

Why the other options are there

  • -7.6078 — kept a factor of two that cancels in the correct rearrangement.
  • -1.9020 — dropped that same factor in the other direction.
  • -4.1843 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Product of Inertia

Example 3
Product of inertia (rectangle) — solve for centroidal x offset — Product of Inertia (3)

A machine part's cross section product of inertia is computed for combined bending. Given area (A) = 46.5000 in^2; centroidal y offset (y_bar) = -4.8000 in; product of inertia (I_xy) = 358.0 in^4, determine the centroidal x offset (x_bar) in in.

Given

  • area(A)=46.5000in2area (A) = 46.5000 in^2
  • centroidalyoffset(ybar)=−4.8000incentroidal y offset (y_bar) = -4.8000 in
  • productofinertia(Ixy)=358.0in4product of inertia (I_xy) = 358.0 in^4

Find

centroidal x offset (x_bar), in in

Start with the thinking

  • The governing relation printed in this handbook section is Product of inertia (rectangle).
  • Everything except x_bar is given, so isolate x_bar 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 product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Section for product of inertiacentroidal axisb = 4h = 6

Figure 3 — schematic for Product of inertia (rectangle) — solve for centroidal x offset — Product of Inertia (3)

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  2. Step 2 — Rearrange symbolically for x_bar:

    xbar=IxyAyˉx_{bar} = \dfrac{I_{xy}}{A \bar{y}}
  3. Step 3 — List the givens: area (A) = 46.5000 in^2, centroidal y offset (y_bar) = -4.8000 in, product of inertia (I_xy) = 358.0 in^4.

  4. Step 4 — Substitute the given values:

    xbar=358.046.5000yˉx_{bar} = \dfrac{358.0}{46.5000 \bar{y}}
  5. Step 5 — Evaluate:

    xbar=−1.6039 inx_{bar} = -1.6039\ \text{in}
  6. Step 6 — Check: returning x_bar = -1.6039 in to

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}

    reproduces the given quantities, and both sides carry the same units.

Answer:
xbar=−1.6039 inx_{bar} = -1.6039\ \text{in}

Why the other options are there

  • -3.2079 — kept a factor of two that cancels in the correct rearrangement.
  • -0.8020 — dropped that same factor in the other direction.
  • -1.7643 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Product of Inertia

Example 4
Product of inertia (rectangle) — solve for product of inertia (case 2) — Product of Inertia (4)

An unsymmetric angle section requires the product of inertia for principal axis analysis. Given area (A) = 56.0000 in^2; centroidal x offset (x_bar) = 4.6000 in; centroidal y offset (y_bar) = -3.8000 in, determine the product of inertia (I_xy) in in^4.

Given

  • area(A)=56.0000in2area (A) = 56.0000 in^2
  • centroidalxoffset(xbar)=4.6000incentroidal x offset (x_bar) = 4.6000 in
  • centroidalyoffset(ybar)=−3.8000incentroidal y offset (y_bar) = -3.8000 in

Find

product of inertia (I_xy), in in^4

Start with the thinking

  • The governing relation printed in this handbook section is Product of inertia (rectangle).
  • Everything except I_xy is given, so isolate I_xy 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 product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Section for product of inertiacentroidal axisb = 4h = 6

Figure 4 — schematic for Product of inertia (rectangle) — solve for product of inertia (case 2) — Product of Inertia (4)

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  2. Step 2 — Rearrange symbolically for I_xy:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  3. Step 3 — List the givens: area (A) = 56.0000 in^2, centroidal x offset (x_bar) = 4.6000 in, centroidal y offset (y_bar) = -3.8000 in.

  4. Step 4 — Substitute the given values:

    Ixy=56.0000xˉyˉI_{xy} = 56.0000 \bar{x} \bar{y}
  5. Step 5 — Evaluate:

    I_{xy} = -978.9\ \text{in^4}
  6. Step 6 — Check: returning I_xy = -978.9 in^4 to

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}

    reproduces the given quantities, and both sides carry the same units.

Answer:
I_{xy} = -978.9\ \text{in^4}

Why the other options are there

  • -1,958 — kept a factor of two that cancels in the correct rearrangement.
  • -489.4 — dropped that same factor in the other direction.
  • -1,077 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Product of Inertia

Example 5
Product of inertia (rectangle) — solve for area (case 2) — Product of Inertia (5)

A composite area's product of inertia about its centroid is needed before rotating axes. Given centroidal x offset (x_bar) = -4.8000 in; centroidal y offset (y_bar) = 0.1000 in; product of inertia (I_xy) = -278.0 in^4, determine the area (A) in in^2.

Given

  • centroidalxoffset(xbar)=−4.8000incentroidal x offset (x_bar) = -4.8000 in
  • centroidalyoffset(ybar)=0.1000incentroidal y offset (y_bar) = 0.1000 in
  • productofinertia(Ixy)=−278.0in4product of inertia (I_xy) = -278.0 in^4

Find

area (A), in in^2

Start with the thinking

  • The governing relation printed in this handbook section is Product of inertia (rectangle).
  • Everything except A is given, so isolate A 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 product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Section for product of inertiacentroidal axisb = 4h = 6

Figure 5 — schematic for Product of inertia (rectangle) — solve for area (case 2) — Product of Inertia (5)

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  2. Step 2 — Rearrange symbolically for A:

    A=Ixyxˉ yˉA = \dfrac{I_{xy}}{\bar{x}\,\bar{y}}
  3. Step 3 — List the givens: centroidal x offset (x_bar) = -4.8000 in, centroidal y offset (y_bar) = 0.1000 in, product of inertia (I_xy) = -278.0 in^4.

  4. Step 4 — Substitute the given values:

    A=−278.0xˉ yˉA = \dfrac{-278.0}{\bar{x}\,\bar{y}}
  5. Step 5 — Evaluate:

    A = 579.2\ \text{in^2}
  6. Step 6 — Check: returning A = 579.2 in^2 to

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}

    reproduces the given quantities, and both sides carry the same units.

Answer:
A = 579.2\ \text{in^2}

Why the other options are there

  • 1,158 — kept a factor of two that cancels in the correct rearrangement.
  • 289.6 — dropped that same factor in the other direction.
  • 637.1 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Product of Inertia

Example 6
Product of inertia (rectangle) — solve for centroidal x offset (case 2) — Product of Inertia (6)

A machine part's cross section product of inertia is computed for combined bending. Given area (A) = 31.5000 in^2; centroidal y offset (y_bar) = -2.0000 in; product of inertia (I_xy) = 329.0 in^4, determine the centroidal x offset (x_bar) in in.

Given

  • area(A)=31.5000in2area (A) = 31.5000 in^2
  • centroidalyoffset(ybar)=−2.0000incentroidal y offset (y_bar) = -2.0000 in
  • productofinertia(Ixy)=329.0in4product of inertia (I_xy) = 329.0 in^4

Find

centroidal x offset (x_bar), in in

Start with the thinking

  • The governing relation printed in this handbook section is Product of inertia (rectangle).
  • Everything except x_bar is given, so isolate x_bar 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 product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Section for product of inertiacentroidal axisb = 4h = 6

Figure 6 — schematic for Product of inertia (rectangle) — solve for centroidal x offset (case 2) — Product of Inertia (6)

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  2. Step 2 — Rearrange symbolically for x_bar:

    xbar=IxyAyˉx_{bar} = \dfrac{I_{xy}}{A \bar{y}}
  3. Step 3 — List the givens: area (A) = 31.5000 in^2, centroidal y offset (y_bar) = -2.0000 in, product of inertia (I_xy) = 329.0 in^4.

  4. Step 4 — Substitute the given values:

    xbar=329.031.5000yˉx_{bar} = \dfrac{329.0}{31.5000 \bar{y}}
  5. Step 5 — Evaluate:

    xbar=−5.2222 inx_{bar} = -5.2222\ \text{in}
  6. Step 6 — Check: returning x_bar = -5.2222 in to

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}

    reproduces the given quantities, and both sides carry the same units.

Answer:
xbar=−5.2222 inx_{bar} = -5.2222\ \text{in}

Why the other options are there

  • -10.4444 — kept a factor of two that cancels in the correct rearrangement.
  • -2.6111 — dropped that same factor in the other direction.
  • -5.7444 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Product of Inertia

Example 7
Product of inertia (rectangle) — solve for product of inertia (case 3) — Product of Inertia (7)

An unsymmetric angle section requires the product of inertia for principal axis analysis. Given area (A) = 58.5000 in^2; centroidal x offset (x_bar) = 4.8000 in; centroidal y offset (y_bar) = 0.9000 in, determine the product of inertia (I_xy) in in^4.

Given

  • area(A)=58.5000in2area (A) = 58.5000 in^2
  • centroidalxoffset(xbar)=4.8000incentroidal x offset (x_bar) = 4.8000 in
  • centroidalyoffset(ybar)=0.9000incentroidal y offset (y_bar) = 0.9000 in

Find

product of inertia (I_xy), in in^4

Start with the thinking

  • The governing relation printed in this handbook section is Product of inertia (rectangle).
  • Everything except I_xy is given, so isolate I_xy 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 product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Section for product of inertiacentroidal axisb = 4h = 6

Figure 7 — schematic for Product of inertia (rectangle) — solve for product of inertia (case 3) — Product of Inertia (7)

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  2. Step 2 — Rearrange symbolically for I_xy:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  3. Step 3 — List the givens: area (A) = 58.5000 in^2, centroidal x offset (x_bar) = 4.8000 in, centroidal y offset (y_bar) = 0.9000 in.

  4. Step 4 — Substitute the given values:

    Ixy=58.5000xˉyˉI_{xy} = 58.5000 \bar{x} \bar{y}
  5. Step 5 — Evaluate:

    I_{xy} = 252.7\ \text{in^4}
  6. Step 6 — Check: returning I_xy = 252.7 in^4 to

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}

    reproduces the given quantities, and both sides carry the same units.

Answer:
I_{xy} = 252.7\ \text{in^4}

Why the other options are there

  • 505.4 — kept a factor of two that cancels in the correct rearrangement.
  • 126.4 — dropped that same factor in the other direction.
  • 278.0 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Product of Inertia

Example 8
Product of inertia (rectangle) — solve for area (case 3) — Product of Inertia (8)

A composite area's product of inertia about its centroid is needed before rotating axes. Given centroidal x offset (x_bar) = 1.8000 in; centroidal y offset (y_bar) = 3.0000 in; product of inertia (I_xy) = -182.0 in^4, determine the area (A) in in^2.

Given

  • centroidalxoffset(xbar)=1.8000incentroidal x offset (x_bar) = 1.8000 in
  • centroidalyoffset(ybar)=3.0000incentroidal y offset (y_bar) = 3.0000 in
  • productofinertia(Ixy)=−182.0in4product of inertia (I_xy) = -182.0 in^4

Find

area (A), in in^2

Start with the thinking

  • The governing relation printed in this handbook section is Product of inertia (rectangle).
  • Everything except A is given, so isolate A 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 product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Section for product of inertiacentroidal axisb = 4h = 6

Figure 8 — schematic for Product of inertia (rectangle) — solve for area (case 3) — Product of Inertia (8)

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  2. Step 2 — Rearrange symbolically for A:

    A=Ixyxˉ yˉA = \dfrac{I_{xy}}{\bar{x}\,\bar{y}}
  3. Step 3 — List the givens: centroidal x offset (x_bar) = 1.8000 in, centroidal y offset (y_bar) = 3.0000 in, product of inertia (I_xy) = -182.0 in^4.

  4. Step 4 — Substitute the given values:

    A=−182.0xˉ yˉA = \dfrac{-182.0}{\bar{x}\,\bar{y}}
  5. Step 5 — Evaluate:

    A = -33.7037\ \text{in^2}
  6. Step 6 — Check: returning A = -33.7037 in^2 to

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}

    reproduces the given quantities, and both sides carry the same units.

Answer:
A = -33.7037\ \text{in^2}

Why the other options are there

  • -67.4074 — kept a factor of two that cancels in the correct rearrangement.
  • -16.8519 — dropped that same factor in the other direction.
  • -37.0741 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Product of Inertia

Example 9
Product of inertia (rectangle) — solve for centroidal x offset (case 3) — Product of Inertia (9)

A machine part's cross section product of inertia is computed for combined bending. Given area (A) = 58.0000 in^2; centroidal y offset (y_bar) = -2.8000 in; product of inertia (I_xy) = 154.0 in^4, determine the centroidal x offset (x_bar) in in.

Given

  • area(A)=58.0000in2area (A) = 58.0000 in^2
  • centroidalyoffset(ybar)=−2.8000incentroidal y offset (y_bar) = -2.8000 in
  • productofinertia(Ixy)=154.0in4product of inertia (I_xy) = 154.0 in^4

Find

centroidal x offset (x_bar), in in

Start with the thinking

  • The governing relation printed in this handbook section is Product of inertia (rectangle).
  • Everything except x_bar is given, so isolate x_bar 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 product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Section for product of inertiacentroidal axisb = 4h = 6

Figure 9 — schematic for Product of inertia (rectangle) — solve for centroidal x offset (case 3) — Product of Inertia (9)

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  2. Step 2 — Rearrange symbolically for x_bar:

    xbar=IxyAyˉx_{bar} = \dfrac{I_{xy}}{A \bar{y}}
  3. Step 3 — List the givens: area (A) = 58.0000 in^2, centroidal y offset (y_bar) = -2.8000 in, product of inertia (I_xy) = 154.0 in^4.

  4. Step 4 — Substitute the given values:

    xbar=154.058.0000yˉx_{bar} = \dfrac{154.0}{58.0000 \bar{y}}
  5. Step 5 — Evaluate:

    xbar=−0.9483 inx_{bar} = -0.9483\ \text{in}
  6. Step 6 — Check: returning x_bar = -0.9483 in to

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}

    reproduces the given quantities, and both sides carry the same units.

Answer:
xbar=−0.9483 inx_{bar} = -0.9483\ \text{in}

Why the other options are there

  • -1.8966 — kept a factor of two that cancels in the correct rearrangement.
  • -0.4741 — dropped that same factor in the other direction.
  • -1.0431 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Product of Inertia

Example 10
Product of inertia (rectangle) — solve for product of inertia (case 4) — Product of Inertia (10)

An unsymmetric angle section requires the product of inertia for principal axis analysis. Given area (A) = 31.5000 in^2; centroidal x offset (x_bar) = 3.6000 in; centroidal y offset (y_bar) = 3.7000 in, determine the product of inertia (I_xy) in in^4.

Given

  • area(A)=31.5000in2area (A) = 31.5000 in^2
  • centroidalxoffset(xbar)=3.6000incentroidal x offset (x_bar) = 3.6000 in
  • centroidalyoffset(ybar)=3.7000incentroidal y offset (y_bar) = 3.7000 in

Find

product of inertia (I_xy), in in^4

Start with the thinking

  • The governing relation printed in this handbook section is Product of inertia (rectangle).
  • Everything except I_xy is given, so isolate I_xy 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 product of inertia of an area about centroidal axes is required for unsymmetric bending and rotated-axis transformations.
Section for product of inertiacentroidal axisb = 4h = 6

Figure 10 — schematic for Product of inertia (rectangle) — solve for product of inertia (case 4) — Product of Inertia (10)

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  2. Step 2 — Rearrange symbolically for I_xy:

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}
  3. Step 3 — List the givens: area (A) = 31.5000 in^2, centroidal x offset (x_bar) = 3.6000 in, centroidal y offset (y_bar) = 3.7000 in.

  4. Step 4 — Substitute the given values:

    Ixy=31.5000xˉyˉI_{xy} = 31.5000 \bar{x} \bar{y}
  5. Step 5 — Evaluate:

    I_{xy} = 419.6\ \text{in^4}
  6. Step 6 — Check: returning I_xy = 419.6 in^4 to

    Ixy=AxˉyˉI_{xy} = A \bar{x} \bar{y}

    reproduces the given quantities, and both sides carry the same units.

Answer:
I_{xy} = 419.6\ \text{in^4}

Why the other options are there

  • 839.2 — kept a factor of two that cancels in the correct rearrangement.
  • 209.8 — dropped that same factor in the other direction.
  • 461.5 — rounded an intermediate value before the final step.

Reference: FE Handbook — Statics: Product of Inertia

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