x^2+28x+21=0

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Solution for x^2+28x+21=0 equation:


Simplifying
x2 + 28x + 21 = 0

Reorder the terms:
21 + 28x + x2 = 0

Solving
21 + 28x + 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 + 28x + -21 + x2 = 0 + -21

Reorder the terms:
21 + -21 + 28x + x2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + 28x + x2 = 0 + -21
28x + x2 = 0 + -21

Combine like terms: 0 + -21 = -21
28x + x2 = -21

The x term is 28x.  Take half its coefficient (14).
Square it (196) and add it to both sides.

Add '196' to each side of the equation.
28x + 196 + x2 = -21 + 196

Reorder the terms:
196 + 28x + x2 = -21 + 196

Combine like terms: -21 + 196 = 175
196 + 28x + x2 = 175

Factor a perfect square on the left side:
(x + 14)(x + 14) = 175

Calculate the square root of the right side: 13.228756555

Break this problem into two subproblems by setting 
(x + 14) equal to 13.228756555 and -13.228756555.

Subproblem 1

x + 14 = 13.228756555 Simplifying x + 14 = 13.228756555 Reorder the terms: 14 + x = 13.228756555 Solving 14 + x = 13.228756555 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-14' to each side of the equation. 14 + -14 + x = 13.228756555 + -14 Combine like terms: 14 + -14 = 0 0 + x = 13.228756555 + -14 x = 13.228756555 + -14 Combine like terms: 13.228756555 + -14 = -0.771243445 x = -0.771243445 Simplifying x = -0.771243445

Subproblem 2

x + 14 = -13.228756555 Simplifying x + 14 = -13.228756555 Reorder the terms: 14 + x = -13.228756555 Solving 14 + x = -13.228756555 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-14' to each side of the equation. 14 + -14 + x = -13.228756555 + -14 Combine like terms: 14 + -14 = 0 0 + x = -13.228756555 + -14 x = -13.228756555 + -14 Combine like terms: -13.228756555 + -14 = -27.228756555 x = -27.228756555 Simplifying x = -27.228756555

Solution

The solution to the problem is based on the solutions from the subproblems. x = {-0.771243445, -27.228756555}

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