9=r(r-8)

Solution for 9=r(r-8) equation:

Simplifying
9 = r(r + -8)

Reorder the terms:
9 = r(-8 + r)
9 = (-8 * r + r * r)
9 = (-8r + r2)

Solving
9 = -8r + r2

Solving for variable 'r'.

Reorder the terms:
9 + 8r + -1r2 = -8r + 8r + r2 + -1r2

Combine like terms: -8r + 8r = 0
9 + 8r + -1r2 = 0 + r2 + -1r2
9 + 8r + -1r2 = r2 + -1r2

Combine like terms: r2 + -1r2 = 0
9 + 8r + -1r2 = 0

Factor a trinomial.
(9 + -1r)(1 + 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 '(1 + r)' equal to zero and attempt to solve:

Simplifying
1 + r = 0

Solving
1 + r = 0

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

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

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

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

Simplifying
r = -1
Solution
r = {9, -1}