x^2+16x+21=0

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Solution for x^2+16x+21=0 equation:


Simplifying
x2 + 16x + 21 = 0

Reorder the terms:
21 + 16x + x2 = 0

Solving
21 + 16x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + 16x + -21 + x2 = 0 + -21

Reorder the terms:
21 + -21 + 16x + x2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + 16x + x2 = 0 + -21
16x + x2 = 0 + -21

Combine like terms: 0 + -21 = -21
16x + x2 = -21

The x term is 16x.  Take half its coefficient (8).
Square it (64) and add it to both sides.

Add '64' to each side of the equation.
16x + 64 + x2 = -21 + 64

Reorder the terms:
64 + 16x + x2 = -21 + 64

Combine like terms: -21 + 64 = 43
64 + 16x + x2 = 43

Factor a perfect square on the left side:
(x + 8)(x + 8) = 43

Calculate the square root of the right side: 6.557438524

Break this problem into two subproblems by setting 
(x + 8) equal to 6.557438524 and -6.557438524.

Subproblem 1

x + 8 = 6.557438524 Simplifying x + 8 = 6.557438524 Reorder the terms: 8 + x = 6.557438524 Solving 8 + x = 6.557438524 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-8' to each side of the equation. 8 + -8 + x = 6.557438524 + -8 Combine like terms: 8 + -8 = 0 0 + x = 6.557438524 + -8 x = 6.557438524 + -8 Combine like terms: 6.557438524 + -8 = -1.442561476 x = -1.442561476 Simplifying x = -1.442561476

Subproblem 2

x + 8 = -6.557438524 Simplifying x + 8 = -6.557438524 Reorder the terms: 8 + x = -6.557438524 Solving 8 + x = -6.557438524 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-8' to each side of the equation. 8 + -8 + x = -6.557438524 + -8 Combine like terms: 8 + -8 = 0 0 + x = -6.557438524 + -8 x = -6.557438524 + -8 Combine like terms: -6.557438524 + -8 = -14.557438524 x = -14.557438524 Simplifying x = -14.557438524

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-1.442561476, -14.557438524}

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