90=x(x+9)

Solution for 90=x(x+9) equation:

Simplifying
90 = x(x + 9)

Reorder the terms:
90 = x(9 + x)
90 = (9 * x + x * x)
90 = (9x + x2)

Solving
90 = 9x + x2

Solving for variable 'x'.

Reorder the terms:
90 + -9x + -1x2 = 9x + -9x + x2 + -1x2

Combine like terms: 9x + -9x = 0
90 + -9x + -1x2 = 0 + x2 + -1x2
90 + -9x + -1x2 = x2 + -1x2

Combine like terms: x2 + -1x2 = 0
90 + -9x + -1x2 = 0

Factor a trinomial.
(6 + -1x)(15 + x) = 0

Subproblem 1
Set the factor '(6 + -1x)' equal to zero and attempt to solve:

Simplifying
6 + -1x = 0

Solving
6 + -1x = 0

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

Add '-6' to each side of the equation.
6 + -6 + -1x = 0 + -6

Combine like terms: 6 + -6 = 0
0 + -1x = 0 + -6
-1x = 0 + -6

Combine like terms: 0 + -6 = -6
-1x = -6

Divide each side by '-1'.
x = 6

Simplifying
x = 6
Subproblem 2
Set the factor '(15 + x)' equal to zero and attempt to solve:

Simplifying
15 + x = 0

Solving
15 + x = 0

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

Add '-15' to each side of the equation.
15 + -15 + x = 0 + -15

Combine like terms: 15 + -15 = 0
0 + x = 0 + -15
x = 0 + -15

Combine like terms: 0 + -15 = -15
x = -15

Simplifying
x = -15
Solution
x = {6, -15}