21x^2-55x-64=0

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Solution for 21x^2-55x-64=0 equation:


Simplifying
21x2 + -55x + -64 = 0

Reorder the terms:
-64 + -55x + 21x2 = 0

Solving
-64 + -55x + 21x2 = 0

Solving for variable 'x'.

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

Divide each side by '21'.
-3.047619048 + -2.619047619x + x2 = 0

Move the constant term to the right:

Add '3.047619048' to each side of the equation.
-3.047619048 + -2.619047619x + 3.047619048 + x2 = 0 + 3.047619048

Reorder the terms:
-3.047619048 + 3.047619048 + -2.619047619x + x2 = 0 + 3.047619048

Combine like terms: -3.047619048 + 3.047619048 = 0.000000000
0.000000000 + -2.619047619x + x2 = 0 + 3.047619048
-2.619047619x + x2 = 0 + 3.047619048

Combine like terms: 0 + 3.047619048 = 3.047619048
-2.619047619x + x2 = 3.047619048

The x term is -2.619047619x.  Take half its coefficient (-1.30952381).
Square it (1.714852609) and add it to both sides.

Add '1.714852609' to each side of the equation.
-2.619047619x + 1.714852609 + x2 = 3.047619048 + 1.714852609

Reorder the terms:
1.714852609 + -2.619047619x + x2 = 3.047619048 + 1.714852609

Combine like terms: 3.047619048 + 1.714852609 = 4.762471657
1.714852609 + -2.619047619x + x2 = 4.762471657

Factor a perfect square on the left side:
(x + -1.30952381)(x + -1.30952381) = 4.762471657

Calculate the square root of the right side: 2.18230879

Break this problem into two subproblems by setting 
(x + -1.30952381) equal to 2.18230879 and -2.18230879.

Subproblem 1

x + -1.30952381 = 2.18230879 Simplifying x + -1.30952381 = 2.18230879 Reorder the terms: -1.30952381 + x = 2.18230879 Solving -1.30952381 + x = 2.18230879 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.30952381' to each side of the equation. -1.30952381 + 1.30952381 + x = 2.18230879 + 1.30952381 Combine like terms: -1.30952381 + 1.30952381 = 0.00000000 0.00000000 + x = 2.18230879 + 1.30952381 x = 2.18230879 + 1.30952381 Combine like terms: 2.18230879 + 1.30952381 = 3.4918326 x = 3.4918326 Simplifying x = 3.4918326

Subproblem 2

x + -1.30952381 = -2.18230879 Simplifying x + -1.30952381 = -2.18230879 Reorder the terms: -1.30952381 + x = -2.18230879 Solving -1.30952381 + x = -2.18230879 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.30952381' to each side of the equation. -1.30952381 + 1.30952381 + x = -2.18230879 + 1.30952381 Combine like terms: -1.30952381 + 1.30952381 = 0.00000000 0.00000000 + x = -2.18230879 + 1.30952381 x = -2.18230879 + 1.30952381 Combine like terms: -2.18230879 + 1.30952381 = -0.87278498 x = -0.87278498 Simplifying x = -0.87278498

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.4918326, -0.87278498}

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