(y^2-9)+2(y^2-9)-99=0

Solution for (y^2-9)+2(y^2-9)-99=0 equation:

Simplifying
(y2 + -9) + 2(y2 + -9) + -99 = 0

Reorder the terms:
(-9 + y2) + 2(y2 + -9) + -99 = 0

Remove parenthesis around (-9 + y2)
-9 + y2 + 2(y2 + -9) + -99 = 0

Reorder the terms:
-9 + y2 + 2(-9 + y2) + -99 = 0
-9 + y2 + (-9 * 2 + y2 * 2) + -99 = 0
-9 + y2 + (-18 + 2y2) + -99 = 0

Reorder the terms:
-9 + -18 + -99 + y2 + 2y2 = 0

Combine like terms: -9 + -18 = -27
-27 + -99 + y2 + 2y2 = 0

Combine like terms: -27 + -99 = -126
-126 + y2 + 2y2 = 0

Combine like terms: y2 + 2y2 = 3y2
-126 + 3y2 = 0

Solving
-126 + 3y2 = 0

Solving for variable 'y'.

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

Add '126' to each side of the equation.
-126 + 126 + 3y2 = 0 + 126

Combine like terms: -126 + 126 = 0
0 + 3y2 = 0 + 126
3y2 = 0 + 126

Combine like terms: 0 + 126 = 126
3y2 = 126

Divide each side by '3'.
y2 = 42

Simplifying
y2 = 42

Take the square root of each side:
y = {-6.480740698, 6.480740698}