## soty2013 2 years ago Find the rate of change of the area of a circle per second with respect to its radius r when r = 5 cm.

1. soty2013

@ParthKohli

2. ParthKohli

Differentiate $$\pi r^2$$ with respect to $$r$$.

3. ParthKohli

When you find $$f'(r)$$, find $$f'(5)$$

4. soty2013

Thanks

5. ParthKohli

The answer turns out to be the circumference.

Actually shouldn't it be like this, $$A=\pi r^2$$ Since rate of change is associated with 'time' differentiation with respect to 't'- time, $$\frac{dA}{dt}=\pi\frac{dr^2}{dt}=2\pi r\frac{dr}{dt}$$ rate of change in radius should be given