400=x^2+2x^2

Solution for 400=x^2+2x^2 equation:

Simplifying
400 = x2 + 2x2

Combine like terms: x2 + 2x2 = 3x2
400 = 3x2

Solving
400 = 3x2

Solving for variable 'x'.

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

Add '-3x2' to each side of the equation.
400 + -3x2 = 3x2 + -3x2

Combine like terms: 3x2 + -3x2 = 0
400 + -3x2 = 0

Add '-400' to each side of the equation.
400 + -400 + -3x2 = 0 + -400

Combine like terms: 400 + -400 = 0
0 + -3x2 = 0 + -400
-3x2 = 0 + -400

Combine like terms: 0 + -400 = -400
-3x2 = -400

Divide each side by '-3'.
x2 = 133.3333333

Simplifying
x2 = 133.3333333

Take the square root of each side:
x = {-11.547005382, 11.547005382}