Solve for "r"

Question

Equation for a circle is A=2πrh+2πr²

 

h=4r

 

HINT: 'A' will end up on the right side of the equals sign

Answer 1

Given:  A=2πrh+2πr² and h=4r.     Substitute h. 

A=2πr(4r)+2πr²                            Multiply

A=8πr²+2πr²                                Add like terms

A=10πr²                                                   Flip to look better when you solve for r

10πr²=A                                      Divide by 10π

r²=A/(10π)                                   Take square root

r=√(A/(10π))                               You only need the positive root