15r^2+26r-21=0

Solution for 15r^2+26r-21=0 equation:

Simplifying
15r2 + 26r + -21 = 0

Reorder the terms:
-21 + 26r + 15r2 = 0

Solving
-21 + 26r + 15r2 = 0

Solving for variable 'r'.

Factor a trinomial.
(-7 + -3r)(3 + -5r) = 0

Subproblem 1
Set the factor '(-7 + -3r)' equal to zero and attempt to solve:

Simplifying
-7 + -3r = 0

Solving
-7 + -3r = 0

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

Add '7' to each side of the equation.
-7 + 7 + -3r = 0 + 7

Combine like terms: -7 + 7 = 0
0 + -3r = 0 + 7
-3r = 0 + 7

Combine like terms: 0 + 7 = 7
-3r = 7

Divide each side by '-3'.
r = -2.333333333

Simplifying
r = -2.333333333
Subproblem 2
Set the factor '(3 + -5r)' equal to zero and attempt to solve:

Simplifying
3 + -5r = 0

Solving
3 + -5r = 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 + -5r = 0 + -3

Combine like terms: 3 + -3 = 0
0 + -5r = 0 + -3
-5r = 0 + -3

Combine like terms: 0 + -3 = -3
-5r = -3

Divide each side by '-5'.
r = 0.6

Simplifying
r = 0.6
Solution
r = {-2.333333333, 0.6}