0=.5x(5x)-90

Solution for 0=.5x(5x)-90 equation:

Simplifying
0 = 0.5x(5x) + -90

Remove parenthesis around (5x)
0 = 0.5x * 5x + -90

Reorder the terms for easier multiplication:
0 = 0.5 * 5x * x + -90

Multiply 0.5 * 5
0 = 2.5x * x + -90

Multiply x * x
0 = 2.5x2 + -90

Reorder the terms:
0 = -90 + 2.5x2

Solving
0 = -90 + 2.5x2

Solving for variable 'x'.

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

Add '-2.5x2' to each side of the equation.
0 + -2.5x2 = -90 + 2.5x2 + -2.5x2
Remove the zero:
-2.5x2 = -90 + 2.5x2 + -2.5x2

Combine like terms: 2.5x2 + -2.5x2 = 0.0
-2.5x2 = -90 + 0.0
-2.5x2 = -90

Divide each side by '-2.5'.
x2 = 36

Simplifying
x2 = 36

Take the square root of each side:
x = {-6, 6}