x^2-14x-21=0

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Solution for x^2-14x-21=0 equation:


Simplifying
x2 + -14x + -21 = 0

Reorder the terms:
-21 + -14x + x2 = 0

Solving
-21 + -14x + 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 + -14x + 21 + x2 = 0 + 21

Reorder the terms:
-21 + 21 + -14x + x2 = 0 + 21

Combine like terms: -21 + 21 = 0
0 + -14x + x2 = 0 + 21
-14x + x2 = 0 + 21

Combine like terms: 0 + 21 = 21
-14x + x2 = 21

The x term is -14x.  Take half its coefficient (-7).
Square it (49) and add it to both sides.

Add '49' to each side of the equation.
-14x + 49 + x2 = 21 + 49

Reorder the terms:
49 + -14x + x2 = 21 + 49

Combine like terms: 21 + 49 = 70
49 + -14x + x2 = 70

Factor a perfect square on the left side:
(x + -7)(x + -7) = 70

Calculate the square root of the right side: 8.366600265

Break this problem into two subproblems by setting 
(x + -7) equal to 8.366600265 and -8.366600265.

Subproblem 1

x + -7 = 8.366600265 Simplifying x + -7 = 8.366600265 Reorder the terms: -7 + x = 8.366600265 Solving -7 + x = 8.366600265 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '7' to each side of the equation. -7 + 7 + x = 8.366600265 + 7 Combine like terms: -7 + 7 = 0 0 + x = 8.366600265 + 7 x = 8.366600265 + 7 Combine like terms: 8.366600265 + 7 = 15.366600265 x = 15.366600265 Simplifying x = 15.366600265

Subproblem 2

x + -7 = -8.366600265 Simplifying x + -7 = -8.366600265 Reorder the terms: -7 + x = -8.366600265 Solving -7 + x = -8.366600265 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '7' to each side of the equation. -7 + 7 + x = -8.366600265 + 7 Combine like terms: -7 + 7 = 0 0 + x = -8.366600265 + 7 x = -8.366600265 + 7 Combine like terms: -8.366600265 + 7 = -1.366600265 x = -1.366600265 Simplifying x = -1.366600265

Solution

The solution to the problem is based on the solutions from the subproblems. x = {15.366600265, -1.366600265}

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