3x^2-21x-26=0

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Solution for 3x^2-21x-26=0 equation:


Simplifying
3x2 + -21x + -26 = 0

Reorder the terms:
-26 + -21x + 3x2 = 0

Solving
-26 + -21x + 3x2 = 0

Solving for variable 'x'.

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

Divide each side by '3'.
-8.666666667 + -7x + x2 = 0

Move the constant term to the right:

Add '8.666666667' to each side of the equation.
-8.666666667 + -7x + 8.666666667 + x2 = 0 + 8.666666667

Reorder the terms:
-8.666666667 + 8.666666667 + -7x + x2 = 0 + 8.666666667

Combine like terms: -8.666666667 + 8.666666667 = 0.000000000
0.000000000 + -7x + x2 = 0 + 8.666666667
-7x + x2 = 0 + 8.666666667

Combine like terms: 0 + 8.666666667 = 8.666666667
-7x + x2 = 8.666666667

The x term is -7x.  Take half its coefficient (-3.5).
Square it (12.25) and add it to both sides.

Add '12.25' to each side of the equation.
-7x + 12.25 + x2 = 8.666666667 + 12.25

Reorder the terms:
12.25 + -7x + x2 = 8.666666667 + 12.25

Combine like terms: 8.666666667 + 12.25 = 20.916666667
12.25 + -7x + x2 = 20.916666667

Factor a perfect square on the left side:
(x + -3.5)(x + -3.5) = 20.916666667

Calculate the square root of the right side: 4.573474245

Break this problem into two subproblems by setting 
(x + -3.5) equal to 4.573474245 and -4.573474245.

Subproblem 1

x + -3.5 = 4.573474245 Simplifying x + -3.5 = 4.573474245 Reorder the terms: -3.5 + x = 4.573474245 Solving -3.5 + x = 4.573474245 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.5' to each side of the equation. -3.5 + 3.5 + x = 4.573474245 + 3.5 Combine like terms: -3.5 + 3.5 = 0.0 0.0 + x = 4.573474245 + 3.5 x = 4.573474245 + 3.5 Combine like terms: 4.573474245 + 3.5 = 8.073474245 x = 8.073474245 Simplifying x = 8.073474245

Subproblem 2

x + -3.5 = -4.573474245 Simplifying x + -3.5 = -4.573474245 Reorder the terms: -3.5 + x = -4.573474245 Solving -3.5 + x = -4.573474245 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.5' to each side of the equation. -3.5 + 3.5 + x = -4.573474245 + 3.5 Combine like terms: -3.5 + 3.5 = 0.0 0.0 + x = -4.573474245 + 3.5 x = -4.573474245 + 3.5 Combine like terms: -4.573474245 + 3.5 = -1.073474245 x = -1.073474245 Simplifying x = -1.073474245

Solution

The solution to the problem is based on the solutions from the subproblems. x = {8.073474245, -1.073474245}

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