-4r^2+400=0

Solution for -4r^2+400=0 equation:

Simplifying
-4r2 + 400 = 0

Reorder the terms:
400 + -4r2 = 0

Solving
400 + -4r2 = 0

Solving for variable 'r'.

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

Add '-400' to each side of the equation.
400 + -400 + -4r2 = 0 + -400

Combine like terms: 400 + -400 = 0
0 + -4r2 = 0 + -400
-4r2 = 0 + -400

Combine like terms: 0 + -400 = -400
-4r2 = -400

Divide each side by '-4'.
r2 = 100

Simplifying
r2 = 100

Take the square root of each side:
r = {-10, 10}