Asked by ruth

the radius r of a sphere is increasing at a rate of 3cm/min. find the rate of change of the area when r=3cm
Answered by Steve
a = 4πr^2
da/dt = 8πr dr/dt

Now just plug in your numbers.
Answered by ruth
where did 8 come from
Answered by Steve
hello!?

the derivative of r^2 is 2r

4*2 = 8

?!?!?!??
Answered by ruth
ohhhh ya sorry I get it