8x^2-21x+7=0

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Solution for 8x^2-21x+7=0 equation:


Simplifying
8x2 + -21x + 7 = 0

Reorder the terms:
7 + -21x + 8x2 = 0

Solving
7 + -21x + 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'.
0.875 + -2.625x + x2 = 0

Move the constant term to the right:

Add '-0.875' to each side of the equation.
0.875 + -2.625x + -0.875 + x2 = 0 + -0.875

Reorder the terms:
0.875 + -0.875 + -2.625x + x2 = 0 + -0.875

Combine like terms: 0.875 + -0.875 = 0.000
0.000 + -2.625x + x2 = 0 + -0.875
-2.625x + x2 = 0 + -0.875

Combine like terms: 0 + -0.875 = -0.875
-2.625x + x2 = -0.875

The x term is -2.625x.  Take half its coefficient (-1.3125).
Square it (1.72265625) and add it to both sides.

Add '1.72265625' to each side of the equation.
-2.625x + 1.72265625 + x2 = -0.875 + 1.72265625

Reorder the terms:
1.72265625 + -2.625x + x2 = -0.875 + 1.72265625

Combine like terms: -0.875 + 1.72265625 = 0.84765625
1.72265625 + -2.625x + x2 = 0.84765625

Factor a perfect square on the left side:
(x + -1.3125)(x + -1.3125) = 0.84765625

Calculate the square root of the right side: 0.920682491

Break this problem into two subproblems by setting 
(x + -1.3125) equal to 0.920682491 and -0.920682491.

Subproblem 1

x + -1.3125 = 0.920682491 Simplifying x + -1.3125 = 0.920682491 Reorder the terms: -1.3125 + x = 0.920682491 Solving -1.3125 + x = 0.920682491 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.3125' to each side of the equation. -1.3125 + 1.3125 + x = 0.920682491 + 1.3125 Combine like terms: -1.3125 + 1.3125 = 0.0000 0.0000 + x = 0.920682491 + 1.3125 x = 0.920682491 + 1.3125 Combine like terms: 0.920682491 + 1.3125 = 2.233182491 x = 2.233182491 Simplifying x = 2.233182491

Subproblem 2

x + -1.3125 = -0.920682491 Simplifying x + -1.3125 = -0.920682491 Reorder the terms: -1.3125 + x = -0.920682491 Solving -1.3125 + x = -0.920682491 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.3125' to each side of the equation. -1.3125 + 1.3125 + x = -0.920682491 + 1.3125 Combine like terms: -1.3125 + 1.3125 = 0.0000 0.0000 + x = -0.920682491 + 1.3125 x = -0.920682491 + 1.3125 Combine like terms: -0.920682491 + 1.3125 = 0.391817509 x = 0.391817509 Simplifying x = 0.391817509

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.233182491, 0.391817509}

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