x^2-4x-15=8

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Solution for x^2-4x-15=8 equation:


Simplifying
x2 + -4x + -15 = 8

Reorder the terms:
-15 + -4x + x2 = 8

Solving
-15 + -4x + x2 = 8

Solving for variable 'x'.

Reorder the terms:
-15 + -8 + -4x + x2 = 8 + -8

Combine like terms: -15 + -8 = -23
-23 + -4x + x2 = 8 + -8

Combine like terms: 8 + -8 = 0
-23 + -4x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '23' to each side of the equation.
-23 + -4x + 23 + x2 = 0 + 23

Reorder the terms:
-23 + 23 + -4x + x2 = 0 + 23

Combine like terms: -23 + 23 = 0
0 + -4x + x2 = 0 + 23
-4x + x2 = 0 + 23

Combine like terms: 0 + 23 = 23
-4x + x2 = 23

The x term is -4x.  Take half its coefficient (-2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
-4x + 4 + x2 = 23 + 4

Reorder the terms:
4 + -4x + x2 = 23 + 4

Combine like terms: 23 + 4 = 27
4 + -4x + x2 = 27

Factor a perfect square on the left side:
(x + -2)(x + -2) = 27

Calculate the square root of the right side: 5.196152423

Break this problem into two subproblems by setting 
(x + -2) equal to 5.196152423 and -5.196152423.

Subproblem 1

x + -2 = 5.196152423 Simplifying x + -2 = 5.196152423 Reorder the terms: -2 + x = 5.196152423 Solving -2 + x = 5.196152423 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + x = 5.196152423 + 2 Combine like terms: -2 + 2 = 0 0 + x = 5.196152423 + 2 x = 5.196152423 + 2 Combine like terms: 5.196152423 + 2 = 7.196152423 x = 7.196152423 Simplifying x = 7.196152423

Subproblem 2

x + -2 = -5.196152423 Simplifying x + -2 = -5.196152423 Reorder the terms: -2 + x = -5.196152423 Solving -2 + x = -5.196152423 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + x = -5.196152423 + 2 Combine like terms: -2 + 2 = 0 0 + x = -5.196152423 + 2 x = -5.196152423 + 2 Combine like terms: -5.196152423 + 2 = -3.196152423 x = -3.196152423 Simplifying x = -3.196152423

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.196152423, -3.196152423}

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