20=c(c-8)

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

Simplifying
20 = c(c + -8)

Reorder the terms:
20 = c(-8 + c)
20 = (-8 * c + c * c)
20 = (-8c + c2)

Solving
20 = -8c + c2

Solving for variable 'c'.

Reorder the terms:
20 + 8c + -1c2 = -8c + 8c + c2 + -1c2

Combine like terms: -8c + 8c = 0
20 + 8c + -1c2 = 0 + c2 + -1c2
20 + 8c + -1c2 = c2 + -1c2

Combine like terms: c2 + -1c2 = 0
20 + 8c + -1c2 = 0

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

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

Simplifying
10 + -1c = 0

Solving
10 + -1c = 0

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

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

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

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

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

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

Simplifying
2 + c = 0

Solving
2 + c = 0

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

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

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

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

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