8x^2+10x-21=0

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Solution for 8x^2+10x-21=0 equation:


Simplifying
8x2 + 10x + -21 = 0

Reorder the terms:
-21 + 10x + 8x2 = 0

Solving
-21 + 10x + 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'.
-2.625 + 1.25x + x2 = 0

Move the constant term to the right:

Add '2.625' to each side of the equation.
-2.625 + 1.25x + 2.625 + x2 = 0 + 2.625

Reorder the terms:
-2.625 + 2.625 + 1.25x + x2 = 0 + 2.625

Combine like terms: -2.625 + 2.625 = 0.000
0.000 + 1.25x + x2 = 0 + 2.625
1.25x + x2 = 0 + 2.625

Combine like terms: 0 + 2.625 = 2.625
1.25x + x2 = 2.625

The x term is 1.25x.  Take half its coefficient (0.625).
Square it (0.390625) and add it to both sides.

Add '0.390625' to each side of the equation.
1.25x + 0.390625 + x2 = 2.625 + 0.390625

Reorder the terms:
0.390625 + 1.25x + x2 = 2.625 + 0.390625

Combine like terms: 2.625 + 0.390625 = 3.015625
0.390625 + 1.25x + x2 = 3.015625

Factor a perfect square on the left side:
(x + 0.625)(x + 0.625) = 3.015625

Calculate the square root of the right side: 1.736555499

Break this problem into two subproblems by setting 
(x + 0.625) equal to 1.736555499 and -1.736555499.

Subproblem 1

x + 0.625 = 1.736555499 Simplifying x + 0.625 = 1.736555499 Reorder the terms: 0.625 + x = 1.736555499 Solving 0.625 + x = 1.736555499 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.625' to each side of the equation. 0.625 + -0.625 + x = 1.736555499 + -0.625 Combine like terms: 0.625 + -0.625 = 0.000 0.000 + x = 1.736555499 + -0.625 x = 1.736555499 + -0.625 Combine like terms: 1.736555499 + -0.625 = 1.111555499 x = 1.111555499 Simplifying x = 1.111555499

Subproblem 2

x + 0.625 = -1.736555499 Simplifying x + 0.625 = -1.736555499 Reorder the terms: 0.625 + x = -1.736555499 Solving 0.625 + x = -1.736555499 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.625' to each side of the equation. 0.625 + -0.625 + x = -1.736555499 + -0.625 Combine like terms: 0.625 + -0.625 = 0.000 0.000 + x = -1.736555499 + -0.625 x = -1.736555499 + -0.625 Combine like terms: -1.736555499 + -0.625 = -2.361555499 x = -2.361555499 Simplifying x = -2.361555499

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.111555499, -2.361555499}

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