(a-4)(a+4)=20

Solution for (a-4)(a+4)=20 equation:

Simplifying
(a + -4)(a + 4) = 20

Reorder the terms:
(-4 + a)(a + 4) = 20

Reorder the terms:
(-4 + a)(4 + a) = 20

Multiply (-4 + a) * (4 + a)
(-4(4 + a) + a(4 + a)) = 20
((4 * -4 + a * -4) + a(4 + a)) = 20
((-16 + -4a) + a(4 + a)) = 20
(-16 + -4a + (4 * a + a * a)) = 20
(-16 + -4a + (4a + a2)) = 20

Combine like terms: -4a + 4a = 0
(-16 + 0 + a2) = 20
(-16 + a2) = 20

Solving
-16 + a2 = 20

Solving for variable 'a'.

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

Add '16' to each side of the equation.
-16 + 16 + a2 = 20 + 16

Combine like terms: -16 + 16 = 0
0 + a2 = 20 + 16
a2 = 20 + 16

Combine like terms: 20 + 16 = 36
a2 = 36

Simplifying
a2 = 36

Take the square root of each side:
a = {-6, 6}