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Math Help - [SOLVED] calculus volume (disk method)

  1. #1
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    [SOLVED] calculus volume (disk method)

    can somebody let me know wehre i went wrong i doubt i got the right answer.. those dashes are really equal signs, i should of made it bigger.
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  2. #2
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    you guys see where i have a y^7/2..


    i got that by [ y^3/2)^2 ...

    dont i add 3/2 + 4/2 to get that 7/2?? dont u add a power to a power.. or am i just supposed to mulitply?
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  3. #3
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    Hello, Legendsn3verdie!

    Sorry, I don't understand any of your integrals . . .


    Find the volume of: . \begin{Bmatrix}x \:=\:y^{\frac{3}{2}} \\ x \:=\:0 \\ y\:=\:2 \end{Bmatrix} . revolved about the y-axis
    Code:
            |
            |             *
           2+ - - - * - - -
            |:::*
            |:*
            |*
            |
        - - * - - - - - - - - -
            |
    Formula: . V \;=\; \pi\int^b_a \!\!x^2\,dy


    We have: . V \;\;=\;\;\pi\int^2_0\!\! \left(y^{\frac{3}{2}}\right)^2\,dy \;\;=\;\; \pi\int^2_0\!\! y^3\,dy \;\;=\;\;\frac{\pi}{4}y^4\,\bigg]^2_0

    . . . . . . . . . . =\;\;\frac{\pi}{4}(2^4) - \frac{\pi}{4}(0^4) \;\;=\;\;\frac{\pi}{4}(16) \;\;=\;\;\boxed{4\pi}

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  4. #4
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    Quote Originally Posted by Soroban View Post
    Hello, Legendsn3verdie!

    Sorry, I don't understand any of your integrals . . .

    Code:
            |
            |             *
           2+ - - - * - - -
            |:::*
            |:*
            |*
            |
        - - * - - - - - - - - -
            |
    Formula: . V \;=\; \pi\int^b_a \!\!x^2\,dy


    We have: . V \;\;=\;\;\pi\int^2_0\!\! \left(y^{\frac{3}{2}}\right)^2\,dy \;\;=\;\; \pi\int^2_0\!\! y^3\,dy \;\;=\;\;\frac{\pi}{4}y^4\,\bigg]^2_0

    . . . . . . . . . . =\;\;\frac{\pi}{4}(2^4) - \frac{\pi}{4}(0^4) \;\;=\;\;\frac{\pi}{4}(16) \;\;=\;\;\boxed{4\pi}

    ah ha! ty sir!
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