Find h in terms of r and substitute back into SA.
I have trouble with related rate word problems; half of the time I don't know if the formula I'm using is the right one.
For example, In one of the hw problems:
A right circular cone has a height h = 8 ft, and the base radius r is increasing. Find the rate of change of its surface area S with respect to r when r= 6ft.
The textbook provides a formula of the surface area as: (pi) * r * the square root of r^2 + h^2
I know that I have to find dS/dr, but they give me two values, which confuses me
[I'm still trying to learn how to right out problems and formulas using LaTex, I apologize.
would I start with
pi * r * rad(r^2 + h^2) and set it equal to 0, then square both sides? I know it sounds like a dumb question, I just feel nervous in every step I take in these kinds of problems.
*What I did instead was find the surface area, then find h in terms of r. I got (60 - r^2) / r.