80=3.14r^2

Solution for 80=3.14r^2 equation:

Simplifying
80 = 3.14r2

Solving
80 = 3.14r2

Solving for variable 'r'.

Move all terms containing r to the left, all other terms to the right.

Add '-3.14r2' to each side of the equation.
80 + -3.14r2 = 3.14r2 + -3.14r2

Combine like terms: 3.14r2 + -3.14r2 = 0.00
80 + -3.14r2 = 0.00

Add '-80' to each side of the equation.
80 + -80 + -3.14r2 = 0.00 + -80

Combine like terms: 80 + -80 = 0
0 + -3.14r2 = 0.00 + -80
-3.14r2 = 0.00 + -80

Combine like terms: 0.00 + -80 = -80
-3.14r2 = -80

Divide each side by '-3.14'.
r2 = 25.47770701

Simplifying
r2 = 25.47770701

Take the square root of each side:
r = {-5.047544652, 5.047544652}