x^2-(x+1)=21

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Solution for x^2-(x+1)=21 equation:


Simplifying
x2 + -1(x + 1) = 21

Reorder the terms:
x2 + -1(1 + x) = 21
x2 + (1 * -1 + x * -1) = 21
x2 + (-1 + -1x) = 21

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

Solving
-1 + -1x + x2 = 21

Solving for variable 'x'.

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

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

Combine like terms: 21 + -21 = 0
-22 + -1x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '22' to each side of the equation.
-22 + -1x + 22 + x2 = 0 + 22

Reorder the terms:
-22 + 22 + -1x + x2 = 0 + 22

Combine like terms: -22 + 22 = 0
0 + -1x + x2 = 0 + 22
-1x + x2 = 0 + 22

Combine like terms: 0 + 22 = 22
-1x + x2 = 22

The x term is -1x.  Take half its coefficient (-0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
-1x + 0.25 + x2 = 22 + 0.25

Reorder the terms:
0.25 + -1x + x2 = 22 + 0.25

Combine like terms: 22 + 0.25 = 22.25
0.25 + -1x + x2 = 22.25

Factor a perfect square on the left side:
(x + -0.5)(x + -0.5) = 22.25

Calculate the square root of the right side: 4.716990566

Break this problem into two subproblems by setting 
(x + -0.5) equal to 4.716990566 and -4.716990566.

Subproblem 1

x + -0.5 = 4.716990566 Simplifying x + -0.5 = 4.716990566 Reorder the terms: -0.5 + x = 4.716990566 Solving -0.5 + x = 4.716990566 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + x = 4.716990566 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + x = 4.716990566 + 0.5 x = 4.716990566 + 0.5 Combine like terms: 4.716990566 + 0.5 = 5.216990566 x = 5.216990566 Simplifying x = 5.216990566

Subproblem 2

x + -0.5 = -4.716990566 Simplifying x + -0.5 = -4.716990566 Reorder the terms: -0.5 + x = -4.716990566 Solving -0.5 + x = -4.716990566 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + x = -4.716990566 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + x = -4.716990566 + 0.5 x = -4.716990566 + 0.5 Combine like terms: -4.716990566 + 0.5 = -4.216990566 x = -4.216990566 Simplifying x = -4.216990566

Solution

The solution to the problem is based on the solutions from the subproblems. x = {5.216990566, -4.216990566}

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