2x^2-x-15=4

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


Simplifying
2x2 + -1x + -15 = 4

Reorder the terms:
-15 + -1x + 2x2 = 4

Solving
-15 + -1x + 2x2 = 4

Solving for variable 'x'.

Reorder the terms:
-15 + -4 + -1x + 2x2 = 4 + -4

Combine like terms: -15 + -4 = -19
-19 + -1x + 2x2 = 4 + -4

Combine like terms: 4 + -4 = 0
-19 + -1x + 2x2 = 0

Begin completing the square.  Divide all terms by
2 the coefficient of the squared term: 

Divide each side by '2'.
-9.5 + -0.5x + x2 = 0

Move the constant term to the right:

Add '9.5' to each side of the equation.
-9.5 + -0.5x + 9.5 + x2 = 0 + 9.5

Reorder the terms:
-9.5 + 9.5 + -0.5x + x2 = 0 + 9.5

Combine like terms: -9.5 + 9.5 = 0.0
0.0 + -0.5x + x2 = 0 + 9.5
-0.5x + x2 = 0 + 9.5

Combine like terms: 0 + 9.5 = 9.5
-0.5x + x2 = 9.5

The x term is -0.5x.  Take half its coefficient (-0.25).
Square it (0.0625) and add it to both sides.

Add '0.0625' to each side of the equation.
-0.5x + 0.0625 + x2 = 9.5 + 0.0625

Reorder the terms:
0.0625 + -0.5x + x2 = 9.5 + 0.0625

Combine like terms: 9.5 + 0.0625 = 9.5625
0.0625 + -0.5x + x2 = 9.5625

Factor a perfect square on the left side:
(x + -0.25)(x + -0.25) = 9.5625

Calculate the square root of the right side: 3.092329219

Break this problem into two subproblems by setting 
(x + -0.25) equal to 3.092329219 and -3.092329219.

Subproblem 1

x + -0.25 = 3.092329219 Simplifying x + -0.25 = 3.092329219 Reorder the terms: -0.25 + x = 3.092329219 Solving -0.25 + x = 3.092329219 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.25' to each side of the equation. -0.25 + 0.25 + x = 3.092329219 + 0.25 Combine like terms: -0.25 + 0.25 = 0.00 0.00 + x = 3.092329219 + 0.25 x = 3.092329219 + 0.25 Combine like terms: 3.092329219 + 0.25 = 3.342329219 x = 3.342329219 Simplifying x = 3.342329219

Subproblem 2

x + -0.25 = -3.092329219 Simplifying x + -0.25 = -3.092329219 Reorder the terms: -0.25 + x = -3.092329219 Solving -0.25 + x = -3.092329219 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.25' to each side of the equation. -0.25 + 0.25 + x = -3.092329219 + 0.25 Combine like terms: -0.25 + 0.25 = 0.00 0.00 + x = -3.092329219 + 0.25 x = -3.092329219 + 0.25 Combine like terms: -3.092329219 + 0.25 = -2.842329219 x = -2.842329219 Simplifying x = -2.842329219

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.342329219, -2.842329219}

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