20=a(a-8)

Solution for 20=a(a-8) equation:

Simplifying
20 = a(a + -8)

Reorder the terms:
20 = a(-8 + a)
20 = (-8 * a + a * a)
20 = (-8a + a2)

Solving
20 = -8a + a2

Solving for variable 'a'.

Reorder the terms:
20 + 8a + -1a2 = -8a + 8a + a2 + -1a2

Combine like terms: -8a + 8a = 0
20 + 8a + -1a2 = 0 + a2 + -1a2
20 + 8a + -1a2 = a2 + -1a2

Combine like terms: a2 + -1a2 = 0
20 + 8a + -1a2 = 0

Factor a trinomial.
(10 + -1a)(2 + a) = 0

Subproblem 1
Set the factor '(10 + -1a)' equal to zero and attempt to solve:

Simplifying
10 + -1a = 0

Solving
10 + -1a = 0

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

Add '-10' to each side of the equation.
10 + -10 + -1a = 0 + -10

Combine like terms: 10 + -10 = 0
0 + -1a = 0 + -10
-1a = 0 + -10

Combine like terms: 0 + -10 = -10
-1a = -10

Divide each side by '-1'.
a = 10

Simplifying
a = 10
Subproblem 2
Set the factor '(2 + a)' equal to zero and attempt to solve:

Simplifying
2 + a = 0

Solving
2 + a = 0

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

Add '-2' to each side of the equation.
2 + -2 + a = 0 + -2

Combine like terms: 2 + -2 = 0
0 + a = 0 + -2
a = 0 + -2

Combine like terms: 0 + -2 = -2
a = -2

Simplifying
a = -2
Solution
a = {10, -2}