SOLUTION: The surface area A of a right circular cylinder is A=2Pi times the radius square + 2Pi times the radius times the height and "h" is the height. Find the radius of a right circular

Click here to see ALL problems on Surface-area

Question 44480: The surface area A of a right circular cylinder is A=2Pi times the radius square + 2Pi times the radius times the height and "h" is the height. Find the radius of a right circular cylinder whose surface area is 96.3Pi square inches and whose height is 11.7 inches.
Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
The surface area A of a right circular cylinder is A=2Pi times the radius square + 2Pi times the radius times the height and "h" is the height. Find the radius of a right circular cylinder whose surface area is 96.3Pi square inches and whose height is 11.7 inches.
A=2pir^2+2pirh
96.3pi=2pi(r^2+11.7r)
48.15=r^2+11.7r
100r^2+1170r-4815=0

Solved by pluggable solver: SOLVE quadratic equation with variable

Quadratic equation (in our case ) has the following solutons:

For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=3294900 is greater than zero. That means that there are two solutions: .

Quadratic expression can be factored:

Again, the answer is: 3.22592970444351, -14.9259297044435. Here's your graph:

Hope this helps
Cheers,
Stan H.