## Mimi_x3 3 years ago The volume of a sphere radius r increases at 12pi cm^3/minute by inflation. What is the rate of growth of its surface area?

1. Mimi_x3

Noo..? This is a maths question.

2. imranmeah91

This is what's called related rate problem

3. Mimi_x3

rate of change.

4. imranmeah91

volume of sphere = 4/3 Pi r^3

5. moneybird

|dw:1324353965977:dw|

6. Mimi_x3

I know, i got stuck, there's not enough info :/

7. moneybird

first find the derivative of V first

8. Mimi_x3

I already know. I got stuck in dA/dt = 8pi3*dr/dt There's not enough info.

9. joemath314159

10. joemath314159

youre*

11. Mimi_x3

I found that the radius is sqrt(3)

12. joemath314159

how did you come about that? there is no volume given

13. moneybird

i mean the derivative of volume

14. imranmeah91

write equation relating volume to surface area v= 4/3 Pi r^3 S= 4 Pi r^2 v= s/3 r dv/ds= 1/3r dv= 1/3 r ds

15. joemath314159

We would still need r though right? or do you think they want the answer in terms of r?

16. joemath314159

boo i already gave you a medal lolol

17. Hero

Mimi skipped basic math and went straight to calculus.

18. Mimi_x3

Shut up Hero, people don't need to know that i dont know basic maths. v= s/3r? where did that come from?

19. imranmeah91

*minor correction v= 4/3 Pi r^3 S= 4 Pi r^2 v= (s r)/3 dv/ds= r/3 dv= r/3 ds (12*3 Pi)/r= ds

20. Mimi_x3

ty.