0.8x^2-2.1x-3.5=0

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Solution for 0.8x^2-2.1x-3.5=0 equation:


Simplifying
0.8x2 + -2.1x + -3.5 = 0

Reorder the terms:
-3.5 + -2.1x + 0.8x2 = 0

Solving
-3.5 + -2.1x + 0.8x2 = 0

Solving for variable 'x'.

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

Divide each side by '0.8'.
-4.375 + -2.625x + x2 = 0

Move the constant term to the right:

Add '4.375' to each side of the equation.
-4.375 + -2.625x + 4.375 + x2 = 0 + 4.375

Reorder the terms:
-4.375 + 4.375 + -2.625x + x2 = 0 + 4.375

Combine like terms: -4.375 + 4.375 = 0.000
0.000 + -2.625x + x2 = 0 + 4.375
-2.625x + x2 = 0 + 4.375

Combine like terms: 0 + 4.375 = 4.375
-2.625x + x2 = 4.375

The x term is -2.625x.  Take half its coefficient (-1.3125).
Square it (1.72265625) and add it to both sides.

Add '1.72265625' to each side of the equation.
-2.625x + 1.72265625 + x2 = 4.375 + 1.72265625

Reorder the terms:
1.72265625 + -2.625x + x2 = 4.375 + 1.72265625

Combine like terms: 4.375 + 1.72265625 = 6.09765625
1.72265625 + -2.625x + x2 = 6.09765625

Factor a perfect square on the left side:
(x + -1.3125)(x + -1.3125) = 6.09765625

Calculate the square root of the right side: 2.469343283

Break this problem into two subproblems by setting 
(x + -1.3125) equal to 2.469343283 and -2.469343283.

Subproblem 1

x + -1.3125 = 2.469343283 Simplifying x + -1.3125 = 2.469343283 Reorder the terms: -1.3125 + x = 2.469343283 Solving -1.3125 + x = 2.469343283 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.3125' to each side of the equation. -1.3125 + 1.3125 + x = 2.469343283 + 1.3125 Combine like terms: -1.3125 + 1.3125 = 0.0000 0.0000 + x = 2.469343283 + 1.3125 x = 2.469343283 + 1.3125 Combine like terms: 2.469343283 + 1.3125 = 3.781843283 x = 3.781843283 Simplifying x = 3.781843283

Subproblem 2

x + -1.3125 = -2.469343283 Simplifying x + -1.3125 = -2.469343283 Reorder the terms: -1.3125 + x = -2.469343283 Solving -1.3125 + x = -2.469343283 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.3125' to each side of the equation. -1.3125 + 1.3125 + x = -2.469343283 + 1.3125 Combine like terms: -1.3125 + 1.3125 = 0.0000 0.0000 + x = -2.469343283 + 1.3125 x = -2.469343283 + 1.3125 Combine like terms: -2.469343283 + 1.3125 = -1.156843283 x = -1.156843283 Simplifying x = -1.156843283

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.781843283, -1.156843283}

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