Math
posted by Nancy on .
the formula for the surface area of a cylinder is: A=2πrh+2πr^2 If the height of the cylinder is 10 inches, and the surface area is 200 sq. inches, determine the length of the radius

A = 2 ð r h + 2 ð r ^ 2
2 ð r 10 + 2 ð r ^ 2 = 200 Divide both sides by 2 ð
10 r + r ^ 2 = 100 / ð
r ^ 2 + 10 r  100 / ð = 0
100 / ð = 31.831
Y>ou nust solve equation :
r ^ 2 + 10 r  31.831 = 0
The solutions are :
2.54 in
and  12.54 in
Radius can't be negative, so soution are:
r = 2.54 in
P.S.
If you don't know how to solve equation
In google type:
quadratic equation online
When you see list of results click on:
Free Online Quadratic Equation Solver:Solve by Quadratic Formula
When page be open in rectangle type:
r ^ 2 + 10 r  31.831 = 0
and click option: solve it
You will see solution stepby step 
ð = pi