b^2-2b-21=-6

Solution for b^2-2b-21=-6 equation:

Simplifying
b2 + -2b + -21 = -6

Reorder the terms:
-21 + -2b + b2 = -6

Solving
-21 + -2b + b2 = -6

Solving for variable 'b'.

Reorder the terms:
-21 + 6 + -2b + b2 = -6 + 6

Combine like terms: -21 + 6 = -15
-15 + -2b + b2 = -6 + 6

Combine like terms: -6 + 6 = 0
-15 + -2b + b2 = 0

Factor a trinomial.
(-3 + -1b)(5 + -1b) = 0

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

Simplifying
-3 + -1b = 0

Solving
-3 + -1b = 0

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

Add '3' to each side of the equation.
-3 + 3 + -1b = 0 + 3

Combine like terms: -3 + 3 = 0
0 + -1b = 0 + 3
-1b = 0 + 3

Combine like terms: 0 + 3 = 3
-1b = 3

Divide each side by '-1'.
b = -3

Simplifying
b = -3
Subproblem 2
Set the factor '(5 + -1b)' equal to zero and attempt to solve:

Simplifying
5 + -1b = 0

Solving
5 + -1b = 0

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

Add '-5' to each side of the equation.
5 + -5 + -1b = 0 + -5

Combine like terms: 5 + -5 = 0
0 + -1b = 0 + -5
-1b = 0 + -5

Combine like terms: 0 + -5 = -5
-1b = -5

Divide each side by '-1'.
b = 5

Simplifying
b = 5
Solution
b = {-3, 5}