# Optimization

• Jan 27th 2008, 08:02 AM
doctorgk
Optimization
A solid is formed by adjoining two hemispheres to the ends of a right circular cylinder. The total volume of the solid is 12 cubic centimeters. Find the radius of the cylinder that produces the minimum surface area.

Thank You
• Jan 27th 2008, 09:32 AM
Henderson
Since $$V = \frac {4}{3} \pi r^3 + \pi r^2 h$$,

$$12 = \frac {4}{3} \pi r^3 + \pi r^2 h$$ and
$h = \frac {12}{\frac {4}{3} \pi r^3 + \pi r^2}$

Also, $SA = 4 \pi r^2 + 2 \pi rh$, which is

$SA = 4 \pi r^2 + 2 \pi r \frac {12}{\frac {4}{3} \pi r^3 + \pi r^2}$.

Simplify, derive, set equal to zero, and solve.