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    • Thread Starter

    Hey, can you check my working for this question please. :

    "The volume of a sphere is increasing at a rate of 75cm^3/s. Find the rate at which the radius is increasing at the instant when the radius of the sphere is 15cm."

    My working :

    dv/dt = 75

    v = 4/3*pi*r^3

    dv/dr = 4*pi*r^2

    dr/dt = dr/dv * dv/dt

    Therefore dr/dt = 75/(4*pi*r^2)

    When r = 15

    dr/dt = 0.0265

    Is this right? any comments will be appreciated. Thanks.

    looks right to me (but i've not checked things like your muliplication)

    good luck tomorrow!

    lou xxx

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