s^2+12s+21=0

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Solution for s^2+12s+21=0 equation:


Simplifying
s2 + 12s + 21 = 0

Reorder the terms:
21 + 12s + s2 = 0

Solving
21 + 12s + s2 = 0

Solving for variable 's'.

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + 12s + -21 + s2 = 0 + -21

Reorder the terms:
21 + -21 + 12s + s2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + 12s + s2 = 0 + -21
12s + s2 = 0 + -21

Combine like terms: 0 + -21 = -21
12s + s2 = -21

The s term is 12s.  Take half its coefficient (6).
Square it (36) and add it to both sides.

Add '36' to each side of the equation.
12s + 36 + s2 = -21 + 36

Reorder the terms:
36 + 12s + s2 = -21 + 36

Combine like terms: -21 + 36 = 15
36 + 12s + s2 = 15

Factor a perfect square on the left side:
(s + 6)(s + 6) = 15

Calculate the square root of the right side: 3.872983346

Break this problem into two subproblems by setting 
(s + 6) equal to 3.872983346 and -3.872983346.

Subproblem 1

s + 6 = 3.872983346 Simplifying s + 6 = 3.872983346 Reorder the terms: 6 + s = 3.872983346 Solving 6 + s = 3.872983346 Solving for variable 's'. Move all terms containing s to the left, all other terms to the right. Add '-6' to each side of the equation. 6 + -6 + s = 3.872983346 + -6 Combine like terms: 6 + -6 = 0 0 + s = 3.872983346 + -6 s = 3.872983346 + -6 Combine like terms: 3.872983346 + -6 = -2.127016654 s = -2.127016654 Simplifying s = -2.127016654

Subproblem 2

s + 6 = -3.872983346 Simplifying s + 6 = -3.872983346 Reorder the terms: 6 + s = -3.872983346 Solving 6 + s = -3.872983346 Solving for variable 's'. Move all terms containing s to the left, all other terms to the right. Add '-6' to each side of the equation. 6 + -6 + s = -3.872983346 + -6 Combine like terms: 6 + -6 = 0 0 + s = -3.872983346 + -6 s = -3.872983346 + -6 Combine like terms: -3.872983346 + -6 = -9.872983346 s = -9.872983346 Simplifying s = -9.872983346

Solution

The solution to the problem is based on the solutions from the subproblems. s = {-2.127016654, -9.872983346}

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