13x^2-80x-81=0

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Solution for 13x^2-80x-81=0 equation:


Simplifying
13x2 + -80x + -81 = 0

Reorder the terms:
-81 + -80x + 13x2 = 0

Solving
-81 + -80x + 13x2 = 0

Solving for variable 'x'.

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

Divide each side by '13'.
-6.230769231 + -6.153846154x + x2 = 0

Move the constant term to the right:

Add '6.230769231' to each side of the equation.
-6.230769231 + -6.153846154x + 6.230769231 + x2 = 0 + 6.230769231

Reorder the terms:
-6.230769231 + 6.230769231 + -6.153846154x + x2 = 0 + 6.230769231

Combine like terms: -6.230769231 + 6.230769231 = 0.000000000
0.000000000 + -6.153846154x + x2 = 0 + 6.230769231
-6.153846154x + x2 = 0 + 6.230769231

Combine like terms: 0 + 6.230769231 = 6.230769231
-6.153846154x + x2 = 6.230769231

The x term is -6.153846154x.  Take half its coefficient (-3.076923077).
Square it (9.467455622) and add it to both sides.

Add '9.467455622' to each side of the equation.
-6.153846154x + 9.467455622 + x2 = 6.230769231 + 9.467455622

Reorder the terms:
9.467455622 + -6.153846154x + x2 = 6.230769231 + 9.467455622

Combine like terms: 6.230769231 + 9.467455622 = 15.698224853
9.467455622 + -6.153846154x + x2 = 15.698224853

Factor a perfect square on the left side:
(x + -3.076923077)(x + -3.076923077) = 15.698224853

Calculate the square root of the right side: 3.962098542

Break this problem into two subproblems by setting 
(x + -3.076923077) equal to 3.962098542 and -3.962098542.

Subproblem 1

x + -3.076923077 = 3.962098542 Simplifying x + -3.076923077 = 3.962098542 Reorder the terms: -3.076923077 + x = 3.962098542 Solving -3.076923077 + x = 3.962098542 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.076923077' to each side of the equation. -3.076923077 + 3.076923077 + x = 3.962098542 + 3.076923077 Combine like terms: -3.076923077 + 3.076923077 = 0.000000000 0.000000000 + x = 3.962098542 + 3.076923077 x = 3.962098542 + 3.076923077 Combine like terms: 3.962098542 + 3.076923077 = 7.039021619 x = 7.039021619 Simplifying x = 7.039021619

Subproblem 2

x + -3.076923077 = -3.962098542 Simplifying x + -3.076923077 = -3.962098542 Reorder the terms: -3.076923077 + x = -3.962098542 Solving -3.076923077 + x = -3.962098542 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.076923077' to each side of the equation. -3.076923077 + 3.076923077 + x = -3.962098542 + 3.076923077 Combine like terms: -3.076923077 + 3.076923077 = 0.000000000 0.000000000 + x = -3.962098542 + 3.076923077 x = -3.962098542 + 3.076923077 Combine like terms: -3.962098542 + 3.076923077 = -0.885175465 x = -0.885175465 Simplifying x = -0.885175465

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.039021619, -0.885175465}

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