2.5x^2-x-0.8=0

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Solution for 2.5x^2-x-0.8=0 equation:


Simplifying
2.5x2 + -1x + -0.8 = 0

Reorder the terms:
-0.8 + -1x + 2.5x2 = 0

Solving
-0.8 + -1x + 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'.
-0.32 + -0.4x + x2 = 0

Move the constant term to the right:

Add '0.32' to each side of the equation.
-0.32 + -0.4x + 0.32 + x2 = 0 + 0.32

Reorder the terms:
-0.32 + 0.32 + -0.4x + x2 = 0 + 0.32

Combine like terms: -0.32 + 0.32 = 0.00
0.00 + -0.4x + x2 = 0 + 0.32
-0.4x + x2 = 0 + 0.32

Combine like terms: 0 + 0.32 = 0.32
-0.4x + x2 = 0.32

The x term is -0.4x.  Take half its coefficient (-0.2).
Square it (0.04) and add it to both sides.

Add '0.04' to each side of the equation.
-0.4x + 0.04 + x2 = 0.32 + 0.04

Reorder the terms:
0.04 + -0.4x + x2 = 0.32 + 0.04

Combine like terms: 0.32 + 0.04 = 0.36
0.04 + -0.4x + x2 = 0.36

Factor a perfect square on the left side:
(x + -0.2)(x + -0.2) = 0.36

Calculate the square root of the right side: 0.6

Break this problem into two subproblems by setting 
(x + -0.2) equal to 0.6 and -0.6.

Subproblem 1

x + -0.2 = 0.6 Simplifying x + -0.2 = 0.6 Reorder the terms: -0.2 + x = 0.6 Solving -0.2 + x = 0.6 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.2' to each side of the equation. -0.2 + 0.2 + x = 0.6 + 0.2 Combine like terms: -0.2 + 0.2 = 0.0 0.0 + x = 0.6 + 0.2 x = 0.6 + 0.2 Combine like terms: 0.6 + 0.2 = 0.8 x = 0.8 Simplifying x = 0.8

Subproblem 2

x + -0.2 = -0.6 Simplifying x + -0.2 = -0.6 Reorder the terms: -0.2 + x = -0.6 Solving -0.2 + x = -0.6 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.2' to each side of the equation. -0.2 + 0.2 + x = -0.6 + 0.2 Combine like terms: -0.2 + 0.2 = 0.0 0.0 + x = -0.6 + 0.2 x = -0.6 + 0.2 Combine like terms: -0.6 + 0.2 = -0.4 x = -0.4 Simplifying x = -0.4

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.8, -0.4}

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