5x^2-15x-42=0

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Solution for 5x^2-15x-42=0 equation:


Simplifying
5x2 + -15x + -42 = 0

Reorder the terms:
-42 + -15x + 5x2 = 0

Solving
-42 + -15x + 5x2 = 0

Solving for variable 'x'.

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

Divide each side by '5'.
-8.4 + -3x + x2 = 0

Move the constant term to the right:

Add '8.4' to each side of the equation.
-8.4 + -3x + 8.4 + x2 = 0 + 8.4

Reorder the terms:
-8.4 + 8.4 + -3x + x2 = 0 + 8.4

Combine like terms: -8.4 + 8.4 = 0.0
0.0 + -3x + x2 = 0 + 8.4
-3x + x2 = 0 + 8.4

Combine like terms: 0 + 8.4 = 8.4
-3x + x2 = 8.4

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 = 8.4 + 2.25

Reorder the terms:
2.25 + -3x + x2 = 8.4 + 2.25

Combine like terms: 8.4 + 2.25 = 10.65
2.25 + -3x + x2 = 10.65

Factor a perfect square on the left side:
(x + -1.5)(x + -1.5) = 10.65

Calculate the square root of the right side: 3.263433774

Break this problem into two subproblems by setting 
(x + -1.5) equal to 3.263433774 and -3.263433774.

Subproblem 1

x + -1.5 = 3.263433774 Simplifying x + -1.5 = 3.263433774 Reorder the terms: -1.5 + x = 3.263433774 Solving -1.5 + x = 3.263433774 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 = 3.263433774 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x = 3.263433774 + 1.5 x = 3.263433774 + 1.5 Combine like terms: 3.263433774 + 1.5 = 4.763433774 x = 4.763433774 Simplifying x = 4.763433774

Subproblem 2

x + -1.5 = -3.263433774 Simplifying x + -1.5 = -3.263433774 Reorder the terms: -1.5 + x = -3.263433774 Solving -1.5 + x = -3.263433774 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 = -3.263433774 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x = -3.263433774 + 1.5 x = -3.263433774 + 1.5 Combine like terms: -3.263433774 + 1.5 = -1.763433774 x = -1.763433774 Simplifying x = -1.763433774

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.763433774, -1.763433774}

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