-2.1x^2+77.9x-391.8=0

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Solution for -2.1x^2+77.9x-391.8=0 equation:


Simplifying
-2.1x2 + 77.9x + -391.8 = 0

Reorder the terms:
-391.8 + 77.9x + -2.1x2 = 0

Solving
-391.8 + 77.9x + -2.1x2 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
-2.1 the coefficient of the squared term: 

Divide each side by '-2.1'.
186.5714286 + -37.0952381x + x2 = 0

Move the constant term to the right:

Add '-186.5714286' to each side of the equation.
186.5714286 + -37.0952381x + -186.5714286 + x2 = 0 + -186.5714286

Reorder the terms:
186.5714286 + -186.5714286 + -37.0952381x + x2 = 0 + -186.5714286

Combine like terms: 186.5714286 + -186.5714286 = 0.0000000
0.0000000 + -37.0952381x + x2 = 0 + -186.5714286
-37.0952381x + x2 = 0 + -186.5714286

Combine like terms: 0 + -186.5714286 = -186.5714286
-37.0952381x + x2 = -186.5714286

The x term is -37.0952381x.  Take half its coefficient (-18.54761905).
Square it (344.0141724) and add it to both sides.

Add '344.0141724' to each side of the equation.
-37.0952381x + 344.0141724 + x2 = -186.5714286 + 344.0141724

Reorder the terms:
344.0141724 + -37.0952381x + x2 = -186.5714286 + 344.0141724

Combine like terms: -186.5714286 + 344.0141724 = 157.4427438
344.0141724 + -37.0952381x + x2 = 157.4427438

Factor a perfect square on the left side:
(x + -18.54761905)(x + -18.54761905) = 157.4427438

Calculate the square root of the right side: 12.547619049

Break this problem into two subproblems by setting 
(x + -18.54761905) equal to 12.547619049 and -12.547619049.

Subproblem 1

x + -18.54761905 = 12.547619049 Simplifying x + -18.54761905 = 12.547619049 Reorder the terms: -18.54761905 + x = 12.547619049 Solving -18.54761905 + x = 12.547619049 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '18.54761905' to each side of the equation. -18.54761905 + 18.54761905 + x = 12.547619049 + 18.54761905 Combine like terms: -18.54761905 + 18.54761905 = 0.00000000 0.00000000 + x = 12.547619049 + 18.54761905 x = 12.547619049 + 18.54761905 Combine like terms: 12.547619049 + 18.54761905 = 31.095238099 x = 31.095238099 Simplifying x = 31.095238099

Subproblem 2

x + -18.54761905 = -12.547619049 Simplifying x + -18.54761905 = -12.547619049 Reorder the terms: -18.54761905 + x = -12.547619049 Solving -18.54761905 + x = -12.547619049 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '18.54761905' to each side of the equation. -18.54761905 + 18.54761905 + x = -12.547619049 + 18.54761905 Combine like terms: -18.54761905 + 18.54761905 = 0.00000000 0.00000000 + x = -12.547619049 + 18.54761905 x = -12.547619049 + 18.54761905 Combine like terms: -12.547619049 + 18.54761905 = 6.000000001 x = 6.000000001 Simplifying x = 6.000000001

Solution

The solution to the problem is based on the solutions from the subproblems. x = {31.095238099, 6.000000001}

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