a^2-4a-221=0

Solution for a^2-4a-221=0 equation:

Simplifying
a2 + -4a + -221 = 0

Reorder the terms:
-221 + -4a + a2 = 0

Solving
-221 + -4a + a2 = 0

Solving for variable 'a'.

Factor a trinomial.
(-13 + -1a)(17 + -1a) = 0

Subproblem 1
Set the factor '(-13 + -1a)' equal to zero and attempt to solve:

Simplifying
-13 + -1a = 0

Solving
-13 + -1a = 0

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

Add '13' to each side of the equation.
-13 + 13 + -1a = 0 + 13

Combine like terms: -13 + 13 = 0
0 + -1a = 0 + 13
-1a = 0 + 13

Combine like terms: 0 + 13 = 13
-1a = 13

Divide each side by '-1'.
a = -13

Simplifying
a = -13
Subproblem 2
Set the factor '(17 + -1a)' equal to zero and attempt to solve:

Simplifying
17 + -1a = 0

Solving
17 + -1a = 0

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

Add '-17' to each side of the equation.
17 + -17 + -1a = 0 + -17

Combine like terms: 17 + -17 = 0
0 + -1a = 0 + -17
-1a = 0 + -17

Combine like terms: 0 + -17 = -17
-1a = -17

Divide each side by '-1'.
a = 17

Simplifying
a = 17
Solution
a = {-13, 17}