72-r^2=-r

Solution for 72-r^2=-r equation:

Simplifying
72 + -1r2 = -1r

Solving
72 + -1r2 = -1r

Solving for variable 'r'.

Reorder the terms:
72 + r + -1r2 = -1r + r

Combine like terms: -1r + r = 0
72 + r + -1r2 = 0

Factor a trinomial.
(9 + -1r)(8 + r) = 0

Subproblem 1
Set the factor '(9 + -1r)' equal to zero and attempt to solve:

Simplifying
9 + -1r = 0

Solving
9 + -1r = 0

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

Add '-9' to each side of the equation.
9 + -9 + -1r = 0 + -9

Combine like terms: 9 + -9 = 0
0 + -1r = 0 + -9
-1r = 0 + -9

Combine like terms: 0 + -9 = -9
-1r = -9

Divide each side by '-1'.
r = 9

Simplifying
r = 9
Subproblem 2
Set the factor '(8 + r)' equal to zero and attempt to solve:

Simplifying
8 + r = 0

Solving
8 + r = 0

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

Add '-8' to each side of the equation.
8 + -8 + r = 0 + -8

Combine like terms: 8 + -8 = 0
0 + r = 0 + -8
r = 0 + -8

Combine like terms: 0 + -8 = -8
r = -8

Simplifying
r = -8
Solution
r = {9, -8}