(x^2-1)+2(x^2-1)-15=0

Solution for (x^2-1)+2(x^2-1)-15=0 equation:

Simplifying
(x2 + -1) + 2(x2 + -1) + -15 = 0

Reorder the terms:
(-1 + x2) + 2(x2 + -1) + -15 = 0

Remove parenthesis around (-1 + x2)
-1 + x2 + 2(x2 + -1) + -15 = 0

Reorder the terms:
-1 + x2 + 2(-1 + x2) + -15 = 0
-1 + x2 + (-1 * 2 + x2 * 2) + -15 = 0
-1 + x2 + (-2 + 2x2) + -15 = 0

Reorder the terms:
-1 + -2 + -15 + x2 + 2x2 = 0

Combine like terms: -1 + -2 = -3
-3 + -15 + x2 + 2x2 = 0

Combine like terms: -3 + -15 = -18
-18 + x2 + 2x2 = 0

Combine like terms: x2 + 2x2 = 3x2
-18 + 3x2 = 0

Solving
-18 + 3x2 = 0

Solving for variable 'x'.

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

Add '18' to each side of the equation.
-18 + 18 + 3x2 = 0 + 18

Combine like terms: -18 + 18 = 0
0 + 3x2 = 0 + 18
3x2 = 0 + 18

Combine like terms: 0 + 18 = 18
3x2 = 18

Divide each side by '3'.
x2 = 6

Simplifying
x2 = 6

Take the square root of each side:
x = {-2.449489743, 2.449489743}