(f-9)(f+9)=

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

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

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

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

Multiply (-9 + f) * (9 + f)
(-9(9 + f) + f(9 + f)) = 0
((9 * -9 + f * -9) + f(9 + f)) = 0
((-81 + -9f) + f(9 + f)) = 0
(-81 + -9f + (9 * f + f * f)) = 0
(-81 + -9f + (9f + f2)) = 0

Combine like terms: -9f + 9f = 0
(-81 + 0 + f2) = 0
(-81 + f2) = 0

Solving
-81 + f2 = 0

Solving for variable 'f'.

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

Add '81' to each side of the equation.
-81 + 81 + f2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + f2 = 0 + 81
f2 = 0 + 81

Combine like terms: 0 + 81 = 81
f2 = 81

Simplifying
f2 = 81

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