# Thread: Need Help!

1. ## Need Help!

i'm practicing for my upcomming exam and i found few problems that are related to the ch. we r studying. The problem is i dont know how to solve them, nor i have an answer. can any1 plz help and show step by step how to solve this problem. thnx in advance.
here is the picture of the problems:

2. Originally Posted by BryanK
i'm practicing for my upcomming exam and i found few problems that are related to the ch. we r studying. The problem is i dont know how to solve them, nor i have an answer. can any1 plz help and show step by step how to solve this problem. thnx in advance.
here is the picture of the problems:
this is pre-calculus? or did you post in the wrong forum?

Here's how to start the first, the second is similar.

The volume of a sphere is given by: $\displaystyle V = \frac 43 \pi r^3$

differentiating implicitly with respect to time we get: $\displaystyle \frac {dV}{dt} = 4 \pi r^2~ \frac {dr}{dt}$

now you are given $\displaystyle r$ and $\displaystyle \frac {dr}{dt}$ so just plug them in and solve for $\displaystyle \frac {dV}{dt}$

the second is similar, just use the fact that $\displaystyle V = \pi r^2 h$