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

Solution for (a+9)(a-9)=0 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}