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# Calculus/related rates

duckboy81 wrote at 2009-10-30 05:57:45
From the last post:

dV   3 pi r^2 dr

-- = -------- --          <--------- 4 IN DENOMINATOR

dt       4    dt

At the instant in question:  h = 4, so r = 4h/3 = 16/3.  Substituting:

10 = 3 pi (16/3)^2 dr/dt

3 pi 256 dr

10 = -------- --          <--------- 4  NOT IN DENOMINATOR

9     dt

---During the implicit diff, the 4 in the denominator was dropped somehow...

Billy wrote at 2012-12-13 19:26:08
The answer above is incorrect.  The author forgot to add the 4 on the bottom when he plugged 16/3 into the equation.  In actuality, it should be:

10=(3pi(16/3)^2)*dr

4          dt

10=64pi dr

3   dt

30  =dr

64pi  dt

Calculus

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