(a-9)(a+9)=

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

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

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

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

Multiply (-9 + a) * (9 + a)
(-9(9 + a) + a(9 + a)) = 0
((9 * -9 + a * -9) + a(9 + a)) = 0
((-81 + -9a) + a(9 + a)) = 0
(-81 + -9a + (9 * a + a * a)) = 0
(-81 + -9a + (9a + a2)) = 0

Combine like terms: -9a + 9a = 0
(-81 + 0 + a2) = 0
(-81 + a2) = 0

Solving
-81 + a2 = 0

Solving for variable 'a'.

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

Add '81' to each side of the equation.
-81 + 81 + a2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + a2 = 0 + 81
a2 = 0 + 81

Combine like terms: 0 + 81 = 81
a2 = 81

Simplifying
a2 = 81

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