(x+21)*(x-20)=0

Solution for (x+21)*(x-20)=0 equation:

Simplifying
(x + 21)(x + -20) = 0

Reorder the terms:
(21 + x)(x + -20) = 0

Reorder the terms:
(21 + x)(-20 + x) = 0

Multiply (21 + x) * (-20 + x)
(21(-20 + x) + x(-20 + x)) = 0
((-20 * 21 + x * 21) + x(-20 + x)) = 0
((-420 + 21x) + x(-20 + x)) = 0
(-420 + 21x + (-20 * x + x * x)) = 0
(-420 + 21x + (-20x + x2)) = 0

Combine like terms: 21x + -20x = 1x
(-420 + 1x + x2) = 0

Solving
-420 + 1x + x2 = 0

Solving for variable 'x'.

Factor a trinomial.
(-21 + -1x)(20 + -1x) = 0

Subproblem 1
Set the factor '(-21 + -1x)' equal to zero and attempt to solve:

Simplifying
-21 + -1x = 0

Solving
-21 + -1x = 0

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

Add '21' to each side of the equation.
-21 + 21 + -1x = 0 + 21

Combine like terms: -21 + 21 = 0
0 + -1x = 0 + 21
-1x = 0 + 21

Combine like terms: 0 + 21 = 21
-1x = 21

Divide each side by '-1'.
x = -21

Simplifying
x = -21
Subproblem 2
Set the factor '(20 + -1x)' equal to zero and attempt to solve:

Simplifying
20 + -1x = 0

Solving
20 + -1x = 0

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

Add '-20' to each side of the equation.
20 + -20 + -1x = 0 + -20

Combine like terms: 20 + -20 = 0
0 + -1x = 0 + -20
-1x = 0 + -20

Combine like terms: 0 + -20 = -20
-1x = -20

Divide each side by '-1'.
x = 20

Simplifying
x = 20
Solution
x = {-21, 20}