(c-21)(c+21)=0

Solution for (c-21)(c+21)=0 equation:

Simplifying
(c + -21)(c + 21) = 0

Reorder the terms:
(-21 + c)(c + 21) = 0

Reorder the terms:
(-21 + c)(21 + c) = 0

Multiply (-21 + c) * (21 + c)
(-21(21 + c) + c(21 + c)) = 0
((21 * -21 + c * -21) + c(21 + c)) = 0
((-441 + -21c) + c(21 + c)) = 0
(-441 + -21c + (21 * c + c * c)) = 0
(-441 + -21c + (21c + c2)) = 0

Combine like terms: -21c + 21c = 0
(-441 + 0 + c2) = 0
(-441 + c2) = 0

Solving
-441 + c2 = 0

Solving for variable 'c'.

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

Add '441' to each side of the equation.
-441 + 441 + c2 = 0 + 441

Combine like terms: -441 + 441 = 0
0 + c2 = 0 + 441
c2 = 0 + 441

Combine like terms: 0 + 441 = 441
c2 = 441

Simplifying
c2 = 441

Take the square root of each side:
c = {-21, 21}