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}