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Math Help - Related Rates [Balloon]

  1. #1
    Raj
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    Related Rates [Balloon]

    The radius of a speherical balloon is decreasing at a rate of 3.5 cm/s. At what rate is the surface area of the balloon decreasing when the radius is 14cm?

    dr/dt = -3.5 cm/s

    da/dt = ? when r = 14

    Ive used the area of a sphere forumla, derived, plugged in numbers but i'm getting a wrong answer.
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    Question

    Quote Originally Posted by Raj View Post
    Ive used the area of a sphere forumla, derived, plugged in numbers but i'm getting a wrong answer.
    Could you show us your work? We can point out your mistake.
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  3. #3
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    Quote Originally Posted by Raj View Post
    The radius of a speherical balloon is decreasing at a rate of 3.5 cm/s. At what rate is the surface area of the balloon decreasing when the radius is 14cm?

    dr/dt = -3.5 cm/s

    da/dt = ? when r = 14

    Ive used the area of a sphere forumla, derived, plugged in numbers but i'm getting a wrong answer.

    Your set up is correct .

    \frac{dA}{dr}=4\pi r^2

     <br />
=8\pi r=112\pi<br />

    just multiply it with -3.5 to get the answer .
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