x^2+642x-639=0

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Solution for x^2+642x-639=0 equation:


Simplifying
x2 + 642x + -639 = 0

Reorder the terms:
-639 + 642x + x2 = 0

Solving
-639 + 642x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '639' to each side of the equation.
-639 + 642x + 639 + x2 = 0 + 639

Reorder the terms:
-639 + 639 + 642x + x2 = 0 + 639

Combine like terms: -639 + 639 = 0
0 + 642x + x2 = 0 + 639
642x + x2 = 0 + 639

Combine like terms: 0 + 639 = 639
642x + x2 = 639

The x term is 642x.  Take half its coefficient (321).
Square it (103041) and add it to both sides.

Add '103041' to each side of the equation.
642x + 103041 + x2 = 639 + 103041

Reorder the terms:
103041 + 642x + x2 = 639 + 103041

Combine like terms: 639 + 103041 = 103680
103041 + 642x + x2 = 103680

Factor a perfect square on the left side:
(x + 321)(x + 321) = 103680

Calculate the square root of the right side: 321.99378876

Break this problem into two subproblems by setting 
(x + 321) equal to 321.99378876 and -321.99378876.

Subproblem 1

x + 321 = 321.99378876 Simplifying x + 321 = 321.99378876 Reorder the terms: 321 + x = 321.99378876 Solving 321 + x = 321.99378876 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-321' to each side of the equation. 321 + -321 + x = 321.99378876 + -321 Combine like terms: 321 + -321 = 0 0 + x = 321.99378876 + -321 x = 321.99378876 + -321 Combine like terms: 321.99378876 + -321 = 0.99378876 x = 0.99378876 Simplifying x = 0.99378876

Subproblem 2

x + 321 = -321.99378876 Simplifying x + 321 = -321.99378876 Reorder the terms: 321 + x = -321.99378876 Solving 321 + x = -321.99378876 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-321' to each side of the equation. 321 + -321 + x = -321.99378876 + -321 Combine like terms: 321 + -321 = 0 0 + x = -321.99378876 + -321 x = -321.99378876 + -321 Combine like terms: -321.99378876 + -321 = -642.99378876 x = -642.99378876 Simplifying x = -642.99378876

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.99378876, -642.99378876}

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