a^2+21a-100=0

Solution for a^2+21a-100=0 equation:

Simplifying
a2 + 21a + -100 = 0

Reorder the terms:
-100 + 21a + a2 = 0

Solving
-100 + 21a + a2 = 0

Solving for variable 'a'.

Factor a trinomial.
(-25 + -1a)(4 + -1a) = 0

Subproblem 1
Set the factor '(-25 + -1a)' equal to zero and attempt to solve:

Simplifying
-25 + -1a = 0

Solving
-25 + -1a = 0

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

Add '25' to each side of the equation.
-25 + 25 + -1a = 0 + 25

Combine like terms: -25 + 25 = 0
0 + -1a = 0 + 25
-1a = 0 + 25

Combine like terms: 0 + 25 = 25
-1a = 25

Divide each side by '-1'.
a = -25

Simplifying
a = -25
Subproblem 2
Set the factor '(4 + -1a)' equal to zero and attempt to solve:

Simplifying
4 + -1a = 0

Solving
4 + -1a = 0

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

Add '-4' to each side of the equation.
4 + -4 + -1a = 0 + -4

Combine like terms: 4 + -4 = 0
0 + -1a = 0 + -4
-1a = 0 + -4

Combine like terms: 0 + -4 = -4
-1a = -4

Divide each side by '-1'.
a = 4

Simplifying
a = 4
Solution
a = {-25, 4}