81-x^2=2x^2

Solution for 81-x^2=2x^2 equation:

Simplifying
81 + -1x2 = 2x2

Solving
81 + -1x2 = 2x2

Solving for variable 'x'.

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

Add '-2x2' to each side of the equation.
81 + -1x2 + -2x2 = 2x2 + -2x2

Combine like terms: -1x2 + -2x2 = -3x2
81 + -3x2 = 2x2 + -2x2

Combine like terms: 2x2 + -2x2 = 0
81 + -3x2 = 0

Add '-81' to each side of the equation.
81 + -81 + -3x2 = 0 + -81

Combine like terms: 81 + -81 = 0
0 + -3x2 = 0 + -81
-3x2 = 0 + -81

Combine like terms: 0 + -81 = -81
-3x2 = -81

Divide each side by '-3'.
x2 = 27

Simplifying
x2 = 27

Take the square root of each side:
x = {-5.196152423, 5.196152423}