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.
(-4 + -1A)(25 + -1A) = 0

Subproblem 1
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
Subproblem 2
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
Solution
A = {-4, 25}