r^2+20r+99=0

Solution for r^2+20r+99=0 equation:

Simplifying
r2 + 20r + 99 = 0

Reorder the terms:
99 + 20r + r2 = 0

Solving
99 + 20r + r2 = 0

Solving for variable 'r'.

Factor a trinomial.
(11 + r)(9 + r) = 0

Subproblem 1
Set the factor '(11 + r)' equal to zero and attempt to solve:

Simplifying
11 + r = 0

Solving
11 + r = 0

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

Add '-11' to each side of the equation.
11 + -11 + r = 0 + -11

Combine like terms: 11 + -11 = 0
0 + r = 0 + -11
r = 0 + -11

Combine like terms: 0 + -11 = -11
r = -11

Simplifying
r = -11
Subproblem 2
Set the factor '(9 + r)' equal to zero and attempt to solve:

Simplifying
9 + r = 0

Solving
9 + r = 0

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

Add '-9' to each side of the equation.
9 + -9 + r = 0 + -9

Combine like terms: 9 + -9 = 0
0 + r = 0 + -9
r = 0 + -9

Combine like terms: 0 + -9 = -9
r = -9

Simplifying
r = -9
Solution
r = {-11, -9}