2.5x^2+4x-128=0

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Solution for 2.5x^2+4x-128=0 equation:


Simplifying
2.5x2 + 4x + -128 = 0

Reorder the terms:
-128 + 4x + 2.5x2 = 0

Solving
-128 + 4x + 2.5x2 = 0

Solving for variable 'x'.

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

Divide each side by '2.5'.
-51.2 + 1.6x + x2 = 0

Move the constant term to the right:

Add '51.2' to each side of the equation.
-51.2 + 1.6x + 51.2 + x2 = 0 + 51.2

Reorder the terms:
-51.2 + 51.2 + 1.6x + x2 = 0 + 51.2

Combine like terms: -51.2 + 51.2 = 0.0
0.0 + 1.6x + x2 = 0 + 51.2
1.6x + x2 = 0 + 51.2

Combine like terms: 0 + 51.2 = 51.2
1.6x + x2 = 51.2

The x term is 1.6x.  Take half its coefficient (0.8).
Square it (0.64) and add it to both sides.

Add '0.64' to each side of the equation.
1.6x + 0.64 + x2 = 51.2 + 0.64

Reorder the terms:
0.64 + 1.6x + x2 = 51.2 + 0.64

Combine like terms: 51.2 + 0.64 = 51.84
0.64 + 1.6x + x2 = 51.84

Factor a perfect square on the left side:
(x + 0.8)(x + 0.8) = 51.84

Calculate the square root of the right side: 7.2

Break this problem into two subproblems by setting 
(x + 0.8) equal to 7.2 and -7.2.

Subproblem 1

x + 0.8 = 7.2 Simplifying x + 0.8 = 7.2 Reorder the terms: 0.8 + x = 7.2 Solving 0.8 + x = 7.2 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.8' to each side of the equation. 0.8 + -0.8 + x = 7.2 + -0.8 Combine like terms: 0.8 + -0.8 = 0.0 0.0 + x = 7.2 + -0.8 x = 7.2 + -0.8 Combine like terms: 7.2 + -0.8 = 6.4 x = 6.4 Simplifying x = 6.4

Subproblem 2

x + 0.8 = -7.2 Simplifying x + 0.8 = -7.2 Reorder the terms: 0.8 + x = -7.2 Solving 0.8 + x = -7.2 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.8' to each side of the equation. 0.8 + -0.8 + x = -7.2 + -0.8 Combine like terms: 0.8 + -0.8 = 0.0 0.0 + x = -7.2 + -0.8 x = -7.2 + -0.8 Combine like terms: -7.2 + -0.8 = -8 x = -8 Simplifying x = -8

Solution

The solution to the problem is based on the solutions from the subproblems. x = {6.4, -8}

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