x^2-0.4x-1.65=0

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Solution for x^2-0.4x-1.65=0 equation:


Simplifying
x2 + -0.4x + -1.65 = 0

Reorder the terms:
-1.65 + -0.4x + x2 = 0

Solving
-1.65 + -0.4x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '1.65' to each side of the equation.
-1.65 + -0.4x + 1.65 + x2 = 0 + 1.65

Reorder the terms:
-1.65 + 1.65 + -0.4x + x2 = 0 + 1.65

Combine like terms: -1.65 + 1.65 = 0.00
0.00 + -0.4x + x2 = 0 + 1.65
-0.4x + x2 = 0 + 1.65

Combine like terms: 0 + 1.65 = 1.65
-0.4x + x2 = 1.65

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 = 1.65 + 0.04

Reorder the terms:
0.04 + -0.4x + x2 = 1.65 + 0.04

Combine like terms: 1.65 + 0.04 = 1.69
0.04 + -0.4x + x2 = 1.69

Factor a perfect square on the left side:
(x + -0.2)(x + -0.2) = 1.69

Calculate the square root of the right side: 1.3

Break this problem into two subproblems by setting 
(x + -0.2) equal to 1.3 and -1.3.

Subproblem 1

x + -0.2 = 1.3 Simplifying x + -0.2 = 1.3 Reorder the terms: -0.2 + x = 1.3 Solving -0.2 + x = 1.3 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 = 1.3 + 0.2 Combine like terms: -0.2 + 0.2 = 0.0 0.0 + x = 1.3 + 0.2 x = 1.3 + 0.2 Combine like terms: 1.3 + 0.2 = 1.5 x = 1.5 Simplifying x = 1.5

Subproblem 2

x + -0.2 = -1.3 Simplifying x + -0.2 = -1.3 Reorder the terms: -0.2 + x = -1.3 Solving -0.2 + x = -1.3 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 = -1.3 + 0.2 Combine like terms: -0.2 + 0.2 = 0.0 0.0 + x = -1.3 + 0.2 x = -1.3 + 0.2 Combine like terms: -1.3 + 0.2 = -1.1 x = -1.1 Simplifying x = -1.1

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.5, -1.1}

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