r^2-18r-40=0

Solution for r^2-18r-40=0 equation:

Simplifying
r2 + -18r + -40 = 0

Reorder the terms:
-40 + -18r + r2 = 0

Solving
-40 + -18r + r2 = 0

Solving for variable 'r'.

Factor a trinomial.
(-2 + -1r)(20 + -1r) = 0

Subproblem 1
Set the factor '(-2 + -1r)' equal to zero and attempt to solve:

Simplifying
-2 + -1r = 0

Solving
-2 + -1r = 0

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

Add '2' to each side of the equation.
-2 + 2 + -1r = 0 + 2

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

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

Divide each side by '-1'.
r = -2

Simplifying
r = -2
Subproblem 2
Set the factor '(20 + -1r)' equal to zero and attempt to solve:

Simplifying
20 + -1r = 0

Solving
20 + -1r = 0

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

Add '-20' to each side of the equation.
20 + -20 + -1r = 0 + -20

Combine like terms: 20 + -20 = 0
0 + -1r = 0 + -20
-1r = 0 + -20

Combine like terms: 0 + -20 = -20
-1r = -20

Divide each side by '-1'.
r = 20

Simplifying
r = 20
Solution
r = {-2, 20}