x^2-2x-1=21

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Solution for x^2-2x-1=21 equation:


Simplifying
x2 + -2x + -1 = 21

Reorder the terms:
-1 + -2x + x2 = 21

Solving
-1 + -2x + x2 = 21

Solving for variable 'x'.

Reorder the terms:
-1 + -21 + -2x + x2 = 21 + -21

Combine like terms: -1 + -21 = -22
-22 + -2x + x2 = 21 + -21

Combine like terms: 21 + -21 = 0
-22 + -2x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '22' to each side of the equation.
-22 + -2x + 22 + x2 = 0 + 22

Reorder the terms:
-22 + 22 + -2x + x2 = 0 + 22

Combine like terms: -22 + 22 = 0
0 + -2x + x2 = 0 + 22
-2x + x2 = 0 + 22

Combine like terms: 0 + 22 = 22
-2x + x2 = 22

The x term is -2x.  Take half its coefficient (-1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
-2x + 1 + x2 = 22 + 1

Reorder the terms:
1 + -2x + x2 = 22 + 1

Combine like terms: 22 + 1 = 23
1 + -2x + x2 = 23

Factor a perfect square on the left side:
(x + -1)(x + -1) = 23

Calculate the square root of the right side: 4.795831523

Break this problem into two subproblems by setting 
(x + -1) equal to 4.795831523 and -4.795831523.

Subproblem 1

x + -1 = 4.795831523 Simplifying x + -1 = 4.795831523 Reorder the terms: -1 + x = 4.795831523 Solving -1 + x = 4.795831523 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + x = 4.795831523 + 1 Combine like terms: -1 + 1 = 0 0 + x = 4.795831523 + 1 x = 4.795831523 + 1 Combine like terms: 4.795831523 + 1 = 5.795831523 x = 5.795831523 Simplifying x = 5.795831523

Subproblem 2

x + -1 = -4.795831523 Simplifying x + -1 = -4.795831523 Reorder the terms: -1 + x = -4.795831523 Solving -1 + x = -4.795831523 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + x = -4.795831523 + 1 Combine like terms: -1 + 1 = 0 0 + x = -4.795831523 + 1 x = -4.795831523 + 1 Combine like terms: -4.795831523 + 1 = -3.795831523 x = -3.795831523 Simplifying x = -3.795831523

Solution

The solution to the problem is based on the solutions from the subproblems. x = {5.795831523, -3.795831523}

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