Volumes with Cross Sections

AP Calculus AB· difficulty 3/5

Base bounded by y=1x2y = 1 - x^2 and y=0y = 0. Cross-sections perpendicular to the xx-axis are squares with side equal to the height of the base (1x21 - x^2). Volume:

  • A

    1615\tfrac{16}{15}

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  • B

    43\tfrac{4}{3}

  • C

    11

  • D

    23\tfrac{2}{3}

Explanation

Side =1x2= 1 - x^2. Area =(1x2)2= (1 - x^2)^2. V=11(1x2)2dx=201(12x2+x4)dx=2(12/3+1/5)=2(8/15)=16/15V = \int_{-1}^{1}(1 - x^2)^2\,dx = 2\int_0^1(1 - 2x^2 + x^4)\,dx = 2(1 - 2/3 + 1/5) = 2(8/15) = 16/15.

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