b^2+21b=100

Solution for b^2+21b=100 equation:

Simplifying
b2 + 21b = 100

Reorder the terms:
21b + b2 = 100

Solving
21b + b2 = 100

Solving for variable 'b'.

Reorder the terms:
-100 + 21b + b2 = 100 + -100

Combine like terms: 100 + -100 = 0
-100 + 21b + b2 = 0

Factor a trinomial.
(-25 + -1b)(4 + -1b) = 0

Subproblem 1
Set the factor '(-25 + -1b)' equal to zero and attempt to solve:

Simplifying
-25 + -1b = 0

Solving
-25 + -1b = 0

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

Add '25' to each side of the equation.
-25 + 25 + -1b = 0 + 25

Combine like terms: -25 + 25 = 0
0 + -1b = 0 + 25
-1b = 0 + 25

Combine like terms: 0 + 25 = 25
-1b = 25

Divide each side by '-1'.
b = -25

Simplifying
b = -25
Subproblem 2
Set the factor '(4 + -1b)' equal to zero and attempt to solve:

Simplifying
4 + -1b = 0

Solving
4 + -1b = 0

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

Add '-4' to each side of the equation.
4 + -4 + -1b = 0 + -4

Combine like terms: 4 + -4 = 0
0 + -1b = 0 + -4
-1b = 0 + -4

Combine like terms: 0 + -4 = -4
-1b = -4

Divide each side by '-1'.
b = 4

Simplifying
b = 4
Solution
b = {-25, 4}