400=3.14r^2

Solution for 400=3.14r^2 equation:

Simplifying
400 = 3.14r2

Solving
400 = 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.
400 + -3.14r2 = 3.14r2 + -3.14r2

Combine like terms: 3.14r2 + -3.14r2 = 0.00
400 + -3.14r2 = 0.00

Add '-400' to each side of the equation.
400 + -400 + -3.14r2 = 0.00 + -400

Combine like terms: 400 + -400 = 0
0 + -3.14r2 = 0.00 + -400
-3.14r2 = 0.00 + -400

Combine like terms: 0.00 + -400 = -400
-3.14r2 = -400

Divide each side by '-3.14'.
r2 = 127.388535

Simplifying
r2 = 127.388535

Take the square root of each side:
r = {-11.286652958, 11.286652958}