x^2-2.1x+0.8=0

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Solution for x^2-2.1x+0.8=0 equation:


Simplifying
x2 + -2.1x + 0.8 = 0

Reorder the terms:
0.8 + -2.1x + x2 = 0

Solving
0.8 + -2.1x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '-0.8' to each side of the equation.
0.8 + -2.1x + -0.8 + x2 = 0 + -0.8

Reorder the terms:
0.8 + -0.8 + -2.1x + x2 = 0 + -0.8

Combine like terms: 0.8 + -0.8 = 0.0
0.0 + -2.1x + x2 = 0 + -0.8
-2.1x + x2 = 0 + -0.8

Combine like terms: 0 + -0.8 = -0.8
-2.1x + x2 = -0.8

The x term is -2.1x.  Take half its coefficient (-1.05).
Square it (1.1025) and add it to both sides.

Add '1.1025' to each side of the equation.
-2.1x + 1.1025 + x2 = -0.8 + 1.1025

Reorder the terms:
1.1025 + -2.1x + x2 = -0.8 + 1.1025

Combine like terms: -0.8 + 1.1025 = 0.3025
1.1025 + -2.1x + x2 = 0.3025

Factor a perfect square on the left side:
(x + -1.05)(x + -1.05) = 0.3025

Calculate the square root of the right side: 0.55

Break this problem into two subproblems by setting 
(x + -1.05) equal to 0.55 and -0.55.

Subproblem 1

x + -1.05 = 0.55 Simplifying x + -1.05 = 0.55 Reorder the terms: -1.05 + x = 0.55 Solving -1.05 + x = 0.55 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.05' to each side of the equation. -1.05 + 1.05 + x = 0.55 + 1.05 Combine like terms: -1.05 + 1.05 = 0.00 0.00 + x = 0.55 + 1.05 x = 0.55 + 1.05 Combine like terms: 0.55 + 1.05 = 1.6 x = 1.6 Simplifying x = 1.6

Subproblem 2

x + -1.05 = -0.55 Simplifying x + -1.05 = -0.55 Reorder the terms: -1.05 + x = -0.55 Solving -1.05 + x = -0.55 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.05' to each side of the equation. -1.05 + 1.05 + x = -0.55 + 1.05 Combine like terms: -1.05 + 1.05 = 0.00 0.00 + x = -0.55 + 1.05 x = -0.55 + 1.05 Combine like terms: -0.55 + 1.05 = 0.5 x = 0.5 Simplifying x = 0.5

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.6, 0.5}

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