2(a^2-4)=90

Solution for 2(a^2-4)=90 equation:

Simplifying
2(a2 + -4) = 90

Reorder the terms:
2(-4 + a2) = 90
(-4 * 2 + a2 * 2) = 90
(-8 + 2a2) = 90

Solving
-8 + 2a2 = 90

Solving for variable 'a'.

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

Add '8' to each side of the equation.
-8 + 8 + 2a2 = 90 + 8

Combine like terms: -8 + 8 = 0
0 + 2a2 = 90 + 8
2a2 = 90 + 8

Combine like terms: 90 + 8 = 98
2a2 = 98

Divide each side by '2'.
a2 = 49

Simplifying
a2 = 49

Take the square root of each side:
a = {-7, 7}