(r+9)(r-9)=

Solution for (r+9)(r-9)= equation:

Simplifying
(r + 9)(r + -9) = 0

Reorder the terms:
(9 + r)(r + -9) = 0

Reorder the terms:
(9 + r)(-9 + r) = 0

Multiply (9 + r) * (-9 + r)
(9(-9 + r) + r(-9 + r)) = 0
((-9 * 9 + r * 9) + r(-9 + r)) = 0
((-81 + 9r) + r(-9 + r)) = 0
(-81 + 9r + (-9 * r + r * r)) = 0
(-81 + 9r + (-9r + r2)) = 0

Combine like terms: 9r + -9r = 0
(-81 + 0 + r2) = 0
(-81 + r2) = 0

Solving
-81 + r2 = 0

Solving for variable 'r'.

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

Add '81' to each side of the equation.
-81 + 81 + r2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + r2 = 0 + 81
r2 = 0 + 81

Combine like terms: 0 + 81 = 81
r2 = 81

Simplifying
r2 = 81

Take the square root of each side:
r = {-9, 9}