(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}