8x^2+11x-42=0

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Solution for 8x^2+11x-42=0 equation:


Simplifying
8x2 + 11x + -42 = 0

Reorder the terms:
-42 + 11x + 8x2 = 0

Solving
-42 + 11x + 8x2 = 0

Solving for variable 'x'.

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

Divide each side by '8'.
-5.25 + 1.375x + x2 = 0

Move the constant term to the right:

Add '5.25' to each side of the equation.
-5.25 + 1.375x + 5.25 + x2 = 0 + 5.25

Reorder the terms:
-5.25 + 5.25 + 1.375x + x2 = 0 + 5.25

Combine like terms: -5.25 + 5.25 = 0.00
0.00 + 1.375x + x2 = 0 + 5.25
1.375x + x2 = 0 + 5.25

Combine like terms: 0 + 5.25 = 5.25
1.375x + x2 = 5.25

The x term is 1.375x.  Take half its coefficient (0.6875).
Square it (0.47265625) and add it to both sides.

Add '0.47265625' to each side of the equation.
1.375x + 0.47265625 + x2 = 5.25 + 0.47265625

Reorder the terms:
0.47265625 + 1.375x + x2 = 5.25 + 0.47265625

Combine like terms: 5.25 + 0.47265625 = 5.72265625
0.47265625 + 1.375x + x2 = 5.72265625

Factor a perfect square on the left side:
(x + 0.6875)(x + 0.6875) = 5.72265625

Calculate the square root of the right side: 2.392207401

Break this problem into two subproblems by setting 
(x + 0.6875) equal to 2.392207401 and -2.392207401.

Subproblem 1

x + 0.6875 = 2.392207401 Simplifying x + 0.6875 = 2.392207401 Reorder the terms: 0.6875 + x = 2.392207401 Solving 0.6875 + x = 2.392207401 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.6875' to each side of the equation. 0.6875 + -0.6875 + x = 2.392207401 + -0.6875 Combine like terms: 0.6875 + -0.6875 = 0.0000 0.0000 + x = 2.392207401 + -0.6875 x = 2.392207401 + -0.6875 Combine like terms: 2.392207401 + -0.6875 = 1.704707401 x = 1.704707401 Simplifying x = 1.704707401

Subproblem 2

x + 0.6875 = -2.392207401 Simplifying x + 0.6875 = -2.392207401 Reorder the terms: 0.6875 + x = -2.392207401 Solving 0.6875 + x = -2.392207401 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.6875' to each side of the equation. 0.6875 + -0.6875 + x = -2.392207401 + -0.6875 Combine like terms: 0.6875 + -0.6875 = 0.0000 0.0000 + x = -2.392207401 + -0.6875 x = -2.392207401 + -0.6875 Combine like terms: -2.392207401 + -0.6875 = -3.079707401 x = -3.079707401 Simplifying x = -3.079707401

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.704707401, -3.079707401}

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