x^2-3x-21=1

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Solution for x^2-3x-21=1 equation:


Simplifying
x2 + -3x + -21 = 1

Reorder the terms:
-21 + -3x + x2 = 1

Solving
-21 + -3x + x2 = 1

Solving for variable 'x'.

Reorder the terms:
-21 + -1 + -3x + x2 = 1 + -1

Combine like terms: -21 + -1 = -22
-22 + -3x + x2 = 1 + -1

Combine like terms: 1 + -1 = 0
-22 + -3x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '22' to each side of the equation.
-22 + -3x + 22 + x2 = 0 + 22

Reorder the terms:
-22 + 22 + -3x + x2 = 0 + 22

Combine like terms: -22 + 22 = 0
0 + -3x + x2 = 0 + 22
-3x + x2 = 0 + 22

Combine like terms: 0 + 22 = 22
-3x + x2 = 22

The x term is -3x.  Take half its coefficient (-1.5).
Square it (2.25) and add it to both sides.

Add '2.25' to each side of the equation.
-3x + 2.25 + x2 = 22 + 2.25

Reorder the terms:
2.25 + -3x + x2 = 22 + 2.25

Combine like terms: 22 + 2.25 = 24.25
2.25 + -3x + x2 = 24.25

Factor a perfect square on the left side:
(x + -1.5)(x + -1.5) = 24.25

Calculate the square root of the right side: 4.924428901

Break this problem into two subproblems by setting 
(x + -1.5) equal to 4.924428901 and -4.924428901.

Subproblem 1

x + -1.5 = 4.924428901 Simplifying x + -1.5 = 4.924428901 Reorder the terms: -1.5 + x = 4.924428901 Solving -1.5 + x = 4.924428901 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.5' to each side of the equation. -1.5 + 1.5 + x = 4.924428901 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x = 4.924428901 + 1.5 x = 4.924428901 + 1.5 Combine like terms: 4.924428901 + 1.5 = 6.424428901 x = 6.424428901 Simplifying x = 6.424428901

Subproblem 2

x + -1.5 = -4.924428901 Simplifying x + -1.5 = -4.924428901 Reorder the terms: -1.5 + x = -4.924428901 Solving -1.5 + x = -4.924428901 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.5' to each side of the equation. -1.5 + 1.5 + x = -4.924428901 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x = -4.924428901 + 1.5 x = -4.924428901 + 1.5 Combine like terms: -4.924428901 + 1.5 = -3.424428901 x = -3.424428901 Simplifying x = -3.424428901

Solution

The solution to the problem is based on the solutions from the subproblems. x = {6.424428901, -3.424428901}

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