15=r^2+2r

Solution for 15=r^2+2r equation:

Simplifying
15 = r2 + 2r

Reorder the terms:
15 = 2r + r2

Solving
15 = 2r + r2

Solving for variable 'r'.

Reorder the terms:
15 + -2r + -1r2 = 2r + -2r + r2 + -1r2

Combine like terms: 2r + -2r = 0
15 + -2r + -1r2 = 0 + r2 + -1r2
15 + -2r + -1r2 = r2 + -1r2

Combine like terms: r2 + -1r2 = 0
15 + -2r + -1r2 = 0

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

Subproblem 1
Set the factor '(3 + -1r)' equal to zero and attempt to solve:

Simplifying
3 + -1r = 0

Solving
3 + -1r = 0

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

Add '-3' to each side of the equation.
3 + -3 + -1r = 0 + -3

Combine like terms: 3 + -3 = 0
0 + -1r = 0 + -3
-1r = 0 + -3

Combine like terms: 0 + -3 = -3
-1r = -3

Divide each side by '-1'.
r = 3

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

Simplifying
5 + r = 0

Solving
5 + r = 0

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

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

Combine like terms: 5 + -5 = 0
0 + r = 0 + -5
r = 0 + -5

Combine like terms: 0 + -5 = -5
r = -5

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