SOLUTION: A circular magnet has an inner radius of r-cm, an outer radius 2cm larger and its depth is the same as the inner radius. If the total volume of the magnet is 120 mulitplied by pi c

Question 988251: A circular magnet has an inner radius of r-cm, an outer radius 2cm larger and its depth is the same as the inner radius. If the total volume of the magnet is 120 mulitplied by pi cm^3, find r.
I have written the equation, but cannot solve it.
V= pi x (r+2)^2 x r - pi x r^2 x r
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
A circular magnet has an inner radius of r-cm, an outer radius 2cm larger and its depth is the same as the inner radius. If the total volume of the magnet is 120 mulitplied by pi cm^3, find r.
I have written the equation, but cannot solve it.
V= pi x (r+2)^2 x r - pi x r^2 x r
just make equal to 120pi

divide thru by pi, multiply r

FOIL (r+2)(r+2)

r^3 cancel so we have

Simplify, divide by 4

A quadratic equation

factors to
(r+6)(r-5) = 0
positive solution
r = 5
:
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