90=3.14r^2

Solution for 90=3.14r^2 equation:

Simplifying
90 = 3.14r2

Solving
90 = 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.
90 + -3.14r2 = 3.14r2 + -3.14r2

Combine like terms: 3.14r2 + -3.14r2 = 0.00
90 + -3.14r2 = 0.00

Add '-90' to each side of the equation.
90 + -90 + -3.14r2 = 0.00 + -90

Combine like terms: 90 + -90 = 0
0 + -3.14r2 = 0.00 + -90
-3.14r2 = 0.00 + -90

Combine like terms: 0.00 + -90 = -90
-3.14r2 = -90

Divide each side by '-3.14'.
r2 = 28.66242038

Simplifying
r2 = 28.66242038

Take the square root of each side:
r = {-5.353729577, 5.353729577}