a^2-20a+99=0

Solution for a^2-20a+99=0 equation:

Simplifying
a2 + -20a + 99 = 0

Reorder the terms:
99 + -20a + a2 = 0

Solving
99 + -20a + a2 = 0

Solving for variable 'a'.

Factor a trinomial.
(9 + -1a)(11 + -1a) = 0

Subproblem 1
Set the factor '(9 + -1a)' equal to zero and attempt to solve:

Simplifying
9 + -1a = 0

Solving
9 + -1a = 0

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

Add '-9' to each side of the equation.
9 + -9 + -1a = 0 + -9

Combine like terms: 9 + -9 = 0
0 + -1a = 0 + -9
-1a = 0 + -9

Combine like terms: 0 + -9 = -9
-1a = -9

Divide each side by '-1'.
a = 9

Simplifying
a = 9
Subproblem 2
Set the factor '(11 + -1a)' equal to zero and attempt to solve:

Simplifying
11 + -1a = 0

Solving
11 + -1a = 0

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

Add '-11' to each side of the equation.
11 + -11 + -1a = 0 + -11

Combine like terms: 11 + -11 = 0
0 + -1a = 0 + -11
-1a = 0 + -11

Combine like terms: 0 + -11 = -11
-1a = -11

Divide each side by '-1'.
a = 11

Simplifying
a = 11
Solution
a = {9, 11}