5x^2-15x-40=0

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Solution for 5x^2-15x-40=0 equation: 


Simplifying
5x2 + -15x + -40 = 0

Reorder the terms:
-40 + -15x + 5x2 = 0

Solving
-40 + -15x + 5x2 = 0

Solving for variable 'x'.

Factor out the Greatest Common Factor (GCF), '5'.
5(-8 + -3x + x2) = 0

Ignore the factor 5.

Subproblem 1
Set the factor '(-8 + -3x + x2)' equal to zero and attempt to solve:

Simplifying
-8 + -3x + x2 = 0

Solving
-8 + -3x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '8' to each side of the equation.
-8 + -3x + 8 + x2 = 0 + 8

Reorder the terms:
-8 + 8 + -3x + x2 = 0 + 8

Combine like terms: -8 + 8 = 0
0 + -3x + x2 = 0 + 8
-3x + x2 = 0 + 8

Combine like terms: 0 + 8 = 8
-3x + x2 = 8

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 + 2.25

Reorder the terms:
2.25 + -3x + x2 = 8 + 2.25

Combine like terms: 8 + 2.25 = 10.25
2.25 + -3x + x2 = 10.25

Factor a perfect square on the left side:
(x + -1.5)(x + -1.5) = 10.25

Calculate the square root of the right side: 3.201562119

Break this problem into two subproblems by setting 
(x + -1.5) equal to 3.201562119 and -3.201562119.


Subproblem 1
x + -1.5 = 3.201562119

Simplifying
x + -1.5 = 3.201562119

Reorder the terms:
-1.5 + x = 3.201562119

Solving
-1.5 + x = 3.201562119

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 = 3.201562119 + 1.5

Combine like terms: -1.5 + 1.5 = 0.0
0.0 + x = 3.201562119 + 1.5
x = 3.201562119 + 1.5

Combine like terms: 3.201562119 + 1.5 = 4.701562119
x = 4.701562119

Simplifying
x = 4.701562119


Subproblem 2
x + -1.5 = -3.201562119

Simplifying
x + -1.5 = -3.201562119

Reorder the terms:
-1.5 + x = -3.201562119

Solving
-1.5 + x = -3.201562119

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 = -3.201562119 + 1.5

Combine like terms: -1.5 + 1.5 = 0.0
0.0 + x = -3.201562119 + 1.5
x = -3.201562119 + 1.5

Combine like terms: -3.201562119 + 1.5 = -1.701562119
x = -1.701562119

Simplifying
x = -1.701562119


Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {4.701562119, -1.701562119}
Solution
x = {4.701562119, -1.701562119}

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