r(r+7)-78=0

Solution for r(r+7)-78=0 equation:

Simplifying
r(r + 7) + -78 = 0

Reorder the terms:
r(7 + r) + -78 = 0
(7 * r + r * r) + -78 = 0
(7r + r2) + -78 = 0

Reorder the terms:
-78 + 7r + r2 = 0

Solving
-78 + 7r + r2 = 0

Solving for variable 'r'.

Factor a trinomial.
(-13 + -1r)(6 + -1r) = 0

Subproblem 1
Set the factor '(-13 + -1r)' equal to zero and attempt to solve:

Simplifying
-13 + -1r = 0

Solving
-13 + -1r = 0

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

Add '13' to each side of the equation.
-13 + 13 + -1r = 0 + 13

Combine like terms: -13 + 13 = 0
0 + -1r = 0 + 13
-1r = 0 + 13

Combine like terms: 0 + 13 = 13
-1r = 13

Divide each side by '-1'.
r = -13

Simplifying
r = -13
Subproblem 2
Set the factor '(6 + -1r)' equal to zero and attempt to solve:

Simplifying
6 + -1r = 0

Solving
6 + -1r = 0

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

Add '-6' to each side of the equation.
6 + -6 + -1r = 0 + -6

Combine like terms: 6 + -6 = 0
0 + -1r = 0 + -6
-1r = 0 + -6

Combine like terms: 0 + -6 = -6
-1r = -6

Divide each side by '-1'.
r = 6

Simplifying
r = 6
Solution
r = {-13, 6}