(x-2)(x+2)-21=0

Solution for (x-2)(x+2)-21=0 equation:

Simplifying
(x + -2)(x + 2) + -21 = 0

Reorder the terms:
(-2 + x)(x + 2) + -21 = 0

Reorder the terms:
(-2 + x)(2 + x) + -21 = 0

Multiply (-2 + x) * (2 + x)
(-2(2 + x) + x(2 + x)) + -21 = 0
((2 * -2 + x * -2) + x(2 + x)) + -21 = 0
((-4 + -2x) + x(2 + x)) + -21 = 0
(-4 + -2x + (2 * x + x * x)) + -21 = 0
(-4 + -2x + (2x + x2)) + -21 = 0

Combine like terms: -2x + 2x = 0
(-4 + 0 + x2) + -21 = 0
(-4 + x2) + -21 = 0

Reorder the terms:
-4 + -21 + x2 = 0

Combine like terms: -4 + -21 = -25
-25 + x2 = 0

Solving
-25 + x2 = 0

Solving for variable 'x'.

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

Add '25' to each side of the equation.
-25 + 25 + x2 = 0 + 25

Combine like terms: -25 + 25 = 0
0 + x2 = 0 + 25
x2 = 0 + 25

Combine like terms: 0 + 25 = 25
x2 = 25

Simplifying
x2 = 25

Take the square root of each side:
x = {-5, 5}