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Find the volume generated when the region bounded by $y=x^3$ and the $x$-axis between $x=2$ and $x=7$ is rotated through $360^{\circ}$ about the $x$-axis.

Here is my attempt is this correct? \begin{align*} y &= x^3 \, , \; 2\le x\le7 \\ V &= \int_a^b \pi y^2 \, dx \\ &= \int_2^7\pi(x^3)^2 \, dx \\ &= \pi\int_2^7x^6 \, dx \\ &= \pi \left[ \frac{x^7}7 \right]_2^7 \\ &= \pi \left( 117649-\frac{128}{7} \right) \\ &= \frac{823415\pi}{7} \end{align*}

  • 4
    Looks good to me.2017-02-03
  • 1
    Yup it's correct: [verification](http://www.wolframalpha.com/input/?i=integrate+pi*x%5E6+from+2+to+7)2017-02-03
  • 2
    [This](http://www.wolframalpha.com/input/?i=rotate+y%3Dx%5E3+around+x+axis+from+x+%3D+2+to+x+%3D+7) is even better.2017-02-03

0 Answers 0