8r^2-7r-15=0

Solution for 8r^2-7r-15=0 equation:

Simplifying
8r2 + -7r + -15 = 0

Reorder the terms:
-15 + -7r + 8r2 = 0

Solving
-15 + -7r + 8r2 = 0

Solving for variable 'r'.

Factor a trinomial.
(-1 + -1r)(15 + -8r) = 0

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

Simplifying
-1 + -1r = 0

Solving
-1 + -1r = 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 + -1r = 0 + 1

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

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

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

Simplifying
r = -1
Subproblem 2
Set the factor '(15 + -8r)' equal to zero and attempt to solve:

Simplifying
15 + -8r = 0

Solving
15 + -8r = 0

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

Add '-15' to each side of the equation.
15 + -15 + -8r = 0 + -15

Combine like terms: 15 + -15 = 0
0 + -8r = 0 + -15
-8r = 0 + -15

Combine like terms: 0 + -15 = -15
-8r = -15

Divide each side by '-8'.
r = 1.875

Simplifying
r = 1.875
Solution
r = {-1, 1.875}