x^2-21x-5=0

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Solution for x^2-21x-5=0 equation:


Simplifying
x2 + -21x + -5 = 0

Reorder the terms:
-5 + -21x + x2 = 0

Solving
-5 + -21x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '5' to each side of the equation.
-5 + -21x + 5 + x2 = 0 + 5

Reorder the terms:
-5 + 5 + -21x + x2 = 0 + 5

Combine like terms: -5 + 5 = 0
0 + -21x + x2 = 0 + 5
-21x + x2 = 0 + 5

Combine like terms: 0 + 5 = 5
-21x + x2 = 5

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 = 5 + 110.25

Reorder the terms:
110.25 + -21x + x2 = 5 + 110.25

Combine like terms: 5 + 110.25 = 115.25
110.25 + -21x + x2 = 115.25

Factor a perfect square on the left side:
(x + -10.5)(x + -10.5) = 115.25

Calculate the square root of the right side: 10.735455277

Break this problem into two subproblems by setting 
(x + -10.5) equal to 10.735455277 and -10.735455277.

Subproblem 1

x + -10.5 = 10.735455277 Simplifying x + -10.5 = 10.735455277 Reorder the terms: -10.5 + x = 10.735455277 Solving -10.5 + x = 10.735455277 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 = 10.735455277 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = 10.735455277 + 10.5 x = 10.735455277 + 10.5 Combine like terms: 10.735455277 + 10.5 = 21.235455277 x = 21.235455277 Simplifying x = 21.235455277

Subproblem 2

x + -10.5 = -10.735455277 Simplifying x + -10.5 = -10.735455277 Reorder the terms: -10.5 + x = -10.735455277 Solving -10.5 + x = -10.735455277 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 = -10.735455277 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = -10.735455277 + 10.5 x = -10.735455277 + 10.5 Combine like terms: -10.735455277 + 10.5 = -0.235455277 x = -0.235455277 Simplifying x = -0.235455277

Solution

The solution to the problem is based on the solutions from the subproblems. x = {21.235455277, -0.235455277}

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