7x^2+2x-81=0

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Solution for 7x^2+2x-81=0 equation:


Simplifying
7x2 + 2x + -81 = 0

Reorder the terms:
-81 + 2x + 7x2 = 0

Solving
-81 + 2x + 7x2 = 0

Solving for variable 'x'.

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

Divide each side by '7'.
-11.57142857 + 0.2857142857x + x2 = 0

Move the constant term to the right:

Add '11.57142857' to each side of the equation.
-11.57142857 + 0.2857142857x + 11.57142857 + x2 = 0 + 11.57142857

Reorder the terms:
-11.57142857 + 11.57142857 + 0.2857142857x + x2 = 0 + 11.57142857

Combine like terms: -11.57142857 + 11.57142857 = 0.00000000
0.00000000 + 0.2857142857x + x2 = 0 + 11.57142857
0.2857142857x + x2 = 0 + 11.57142857

Combine like terms: 0 + 11.57142857 = 11.57142857
0.2857142857x + x2 = 11.57142857

The x term is 0.2857142857x.  Take half its coefficient (0.1428571429).
Square it (0.02040816328) and add it to both sides.

Add '0.02040816328' to each side of the equation.
0.2857142857x + 0.02040816328 + x2 = 11.57142857 + 0.02040816328

Reorder the terms:
0.02040816328 + 0.2857142857x + x2 = 11.57142857 + 0.02040816328

Combine like terms: 11.57142857 + 0.02040816328 = 11.59183673328
0.02040816328 + 0.2857142857x + x2 = 11.59183673328

Factor a perfect square on the left side:
(x + 0.1428571429)(x + 0.1428571429) = 11.59183673328

Calculate the square root of the right side: 3.404678653

Break this problem into two subproblems by setting 
(x + 0.1428571429) equal to 3.404678653 and -3.404678653.

Subproblem 1

x + 0.1428571429 = 3.404678653 Simplifying x + 0.1428571429 = 3.404678653 Reorder the terms: 0.1428571429 + x = 3.404678653 Solving 0.1428571429 + x = 3.404678653 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.1428571429' to each side of the equation. 0.1428571429 + -0.1428571429 + x = 3.404678653 + -0.1428571429 Combine like terms: 0.1428571429 + -0.1428571429 = 0.0000000000 0.0000000000 + x = 3.404678653 + -0.1428571429 x = 3.404678653 + -0.1428571429 Combine like terms: 3.404678653 + -0.1428571429 = 3.2618215101 x = 3.2618215101 Simplifying x = 3.2618215101

Subproblem 2

x + 0.1428571429 = -3.404678653 Simplifying x + 0.1428571429 = -3.404678653 Reorder the terms: 0.1428571429 + x = -3.404678653 Solving 0.1428571429 + x = -3.404678653 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.1428571429' to each side of the equation. 0.1428571429 + -0.1428571429 + x = -3.404678653 + -0.1428571429 Combine like terms: 0.1428571429 + -0.1428571429 = 0.0000000000 0.0000000000 + x = -3.404678653 + -0.1428571429 x = -3.404678653 + -0.1428571429 Combine like terms: -3.404678653 + -0.1428571429 = -3.5475357959 x = -3.5475357959 Simplifying x = -3.5475357959

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.2618215101, -3.5475357959}

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