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AP® Calculus AB · Unit 8 · Topic 8.8

Volumes with Cross Sections: Triangles and Semicircles: Topic Checklist (Calculus AB 8.8)

Specific “I can…” statements for volumes with triangular, semicircular and other cross sections, each linked to the guide section and practice question that tests it.

Work through the list without notes. Use a calculator only where a statement says so. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions. This topic is shared by Calculus AB and Calculus BC.

Understanding

  • I can explain why the volume is still ∫ A dx when the slices are triangles or semicircles. (Guide: “Same integral, new shapes”)
  • I can derive the area of an equilateral triangle of side s, (√3/4)s², using Pythagoras. (Guide: “The area formulas, derived”; Practice Q2)
  • I can explain why a semicircle on side s has area (π/8)s², with radius s/2. (Guide: Figure 1; Practice Q1)
  • I can tell the two isosceles right-triangle cases apart: leg in the base gives s²/2, hypotenuse gives s²/4. (Guide: area table; Practice Q3)

Calculation

  • I can find a volume with triangular or semicircular slices perpendicular to the x-axis. (Guide: Worked example 1; Practice Q1, Q5)
  • I can find a volume with slices perpendicular to the y-axis, writing s in terms of y. (Guide: Worked example 2; Practice Q2, Q7(c))
  • I can use a calculator for the limits and the integral, storing values and giving three decimal places. (Guide: Worked example 3; Practice Q4, Q6(c))
  • I can find a volume from a given area function, or from a triangle with a stated height. (Guide: “Other shapes and given areas”; Practice Q7(a))
  • I can estimate a volume from a table with a trapezoidal sum of cross-sectional areas. (Practice Q6(b))

Reasoning

  • I can explain why the ratio of two volumes on the same base depends only on the shape constants. (Practice Q5(d))
  • I can find an unknown constant from a given volume. (Practice Q7(b))
  • I can explain how these solids differ from solids of revolution in Topic 8.9. (Guide: “Common misconceptions”)

All ticked? Move on to Topic 8.9, Volume with Disc Method: Revolving Around the x- or y-Axis, or return to the Calculus AB roadmap or the Calculus BC roadmap.

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