x^2-21x-56=0

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Solution for x^2-21x-56=0 equation:


Simplifying
x2 + -21x + -56 = 0

Reorder the terms:
-56 + -21x + x2 = 0

Solving
-56 + -21x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '56' to each side of the equation.
-56 + -21x + 56 + x2 = 0 + 56

Reorder the terms:
-56 + 56 + -21x + x2 = 0 + 56

Combine like terms: -56 + 56 = 0
0 + -21x + x2 = 0 + 56
-21x + x2 = 0 + 56

Combine like terms: 0 + 56 = 56
-21x + x2 = 56

The x term is -21x.  Take half its coefficient (-10.5).
Square it (110.25) and add it to both sides.

Add '110.25' to each side of the equation.
-21x + 110.25 + x2 = 56 + 110.25

Reorder the terms:
110.25 + -21x + x2 = 56 + 110.25

Combine like terms: 56 + 110.25 = 166.25
110.25 + -21x + x2 = 166.25

Factor a perfect square on the left side:
(x + -10.5)(x + -10.5) = 166.25

Calculate the square root of the right side: 12.893796958

Break this problem into two subproblems by setting 
(x + -10.5) equal to 12.893796958 and -12.893796958.

Subproblem 1

x + -10.5 = 12.893796958 Simplifying x + -10.5 = 12.893796958 Reorder the terms: -10.5 + x = 12.893796958 Solving -10.5 + x = 12.893796958 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '10.5' to each side of the equation. -10.5 + 10.5 + x = 12.893796958 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = 12.893796958 + 10.5 x = 12.893796958 + 10.5 Combine like terms: 12.893796958 + 10.5 = 23.393796958 x = 23.393796958 Simplifying x = 23.393796958

Subproblem 2

x + -10.5 = -12.893796958 Simplifying x + -10.5 = -12.893796958 Reorder the terms: -10.5 + x = -12.893796958 Solving -10.5 + x = -12.893796958 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '10.5' to each side of the equation. -10.5 + 10.5 + x = -12.893796958 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = -12.893796958 + 10.5 x = -12.893796958 + 10.5 Combine like terms: -12.893796958 + 10.5 = -2.393796958 x = -2.393796958 Simplifying x = -2.393796958

Solution

The solution to the problem is based on the solutions from the subproblems. x = {23.393796958, -2.393796958}

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