12=3.14*r^2

Solution for 12=3.14*r^2 equation:

Simplifying
12 = 3.14r2

Solving
12 = 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.
12 + -3.14r2 = 3.14r2 + -3.14r2

Combine like terms: 3.14r2 + -3.14r2 = 0.00
12 + -3.14r2 = 0.00

Add '-12' to each side of the equation.
12 + -12 + -3.14r2 = 0.00 + -12

Combine like terms: 12 + -12 = 0
0 + -3.14r2 = 0.00 + -12
-3.14r2 = 0.00 + -12

Combine like terms: 0.00 + -12 = -12
-3.14r2 = -12

Divide each side by '-3.14'.
r2 = 3.821656051

Simplifying
r2 = 3.821656051

Take the square root of each side:
r = {-1.954905637, 1.954905637}