15=c(c-2)

Solution for 15=c(c-2) equation:

Simplifying
15 = c(c + -2)

Reorder the terms:
15 = c(-2 + c)
15 = (-2 * c + c * c)
15 = (-2c + c2)

Solving
15 = -2c + c2

Solving for variable 'c'.

Reorder the terms:
15 + 2c + -1c2 = -2c + 2c + c2 + -1c2

Combine like terms: -2c + 2c = 0
15 + 2c + -1c2 = 0 + c2 + -1c2
15 + 2c + -1c2 = c2 + -1c2

Combine like terms: c2 + -1c2 = 0
15 + 2c + -1c2 = 0

Factor a trinomial.
(5 + -1c)(3 + c) = 0

Subproblem 1
Set the factor '(5 + -1c)' equal to zero and attempt to solve:

Simplifying
5 + -1c = 0

Solving
5 + -1c = 0

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

Add '-5' to each side of the equation.
5 + -5 + -1c = 0 + -5

Combine like terms: 5 + -5 = 0
0 + -1c = 0 + -5
-1c = 0 + -5

Combine like terms: 0 + -5 = -5
-1c = -5

Divide each side by '-1'.
c = 5

Simplifying
c = 5
Subproblem 2
Set the factor '(3 + c)' equal to zero and attempt to solve:

Simplifying
3 + c = 0

Solving
3 + c = 0

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

Add '-3' to each side of the equation.
3 + -3 + c = 0 + -3

Combine like terms: 3 + -3 = 0
0 + c = 0 + -3
c = 0 + -3

Combine like terms: 0 + -3 = -3
c = -3

Simplifying
c = -3
Solution
c = {5, -3}