(u+9)(u-9)=

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

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

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

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

Multiply (9 + u) * (-9 + u)
(9(-9 + u) + u(-9 + u)) = 0
((-9 * 9 + u * 9) + u(-9 + u)) = 0
((-81 + 9u) + u(-9 + u)) = 0
(-81 + 9u + (-9 * u + u * u)) = 0
(-81 + 9u + (-9u + u2)) = 0

Combine like terms: 9u + -9u = 0
(-81 + 0 + u2) = 0
(-81 + u2) = 0

Solving
-81 + u2 = 0

Solving for variable 'u'.

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

Add '81' to each side of the equation.
-81 + 81 + u2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + u2 = 0 + 81
u2 = 0 + 81

Combine like terms: 0 + 81 = 81
u2 = 81

Simplifying
u2 = 81

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