x^2-21x-2=0

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


Simplifying
x2 + -21x + -2 = 0

Reorder the terms:
-2 + -21x + x2 = 0

Solving
-2 + -21x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '2' to each side of the equation.
-2 + -21x + 2 + x2 = 0 + 2

Reorder the terms:
-2 + 2 + -21x + x2 = 0 + 2

Combine like terms: -2 + 2 = 0
0 + -21x + x2 = 0 + 2
-21x + x2 = 0 + 2

Combine like terms: 0 + 2 = 2
-21x + x2 = 2

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 = 2 + 110.25

Reorder the terms:
110.25 + -21x + x2 = 2 + 110.25

Combine like terms: 2 + 110.25 = 112.25
110.25 + -21x + x2 = 112.25

Factor a perfect square on the left side:
(x + -10.5)(x + -10.5) = 112.25

Calculate the square root of the right side: 10.59481005

Break this problem into two subproblems by setting 
(x + -10.5) equal to 10.59481005 and -10.59481005.

Subproblem 1

x + -10.5 = 10.59481005 Simplifying x + -10.5 = 10.59481005 Reorder the terms: -10.5 + x = 10.59481005 Solving -10.5 + x = 10.59481005 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 = 10.59481005 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = 10.59481005 + 10.5 x = 10.59481005 + 10.5 Combine like terms: 10.59481005 + 10.5 = 21.09481005 x = 21.09481005 Simplifying x = 21.09481005

Subproblem 2

x + -10.5 = -10.59481005 Simplifying x + -10.5 = -10.59481005 Reorder the terms: -10.5 + x = -10.59481005 Solving -10.5 + x = -10.59481005 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 = -10.59481005 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = -10.59481005 + 10.5 x = -10.59481005 + 10.5 Combine like terms: -10.59481005 + 10.5 = -0.09481005 x = -0.09481005 Simplifying x = -0.09481005

Solution

The solution to the problem is based on the solutions from the subproblems. x = {21.09481005, -0.09481005}

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