4x^2-x^2-81=0

Solution for 4x^2-x^2-81=0 equation:

Simplifying
4x2 + -1x2 + -81 = 0

Reorder the terms:
-81 + 4x2 + -1x2 = 0

Combine like terms: 4x2 + -1x2 = 3x2
-81 + 3x2 = 0

Solving
-81 + 3x2 = 0

Solving for variable 'x'.

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

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}