3x^2-21x-2=0

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


Simplifying
3x2 + -21x + -2 = 0

Reorder the terms:
-2 + -21x + 3x2 = 0

Solving
-2 + -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'.
-0.6666666667 + -7x + x2 = 0

Move the constant term to the right:

Add '0.6666666667' to each side of the equation.
-0.6666666667 + -7x + 0.6666666667 + x2 = 0 + 0.6666666667

Reorder the terms:
-0.6666666667 + 0.6666666667 + -7x + x2 = 0 + 0.6666666667

Combine like terms: -0.6666666667 + 0.6666666667 = 0.0000000000
0.0000000000 + -7x + x2 = 0 + 0.6666666667
-7x + x2 = 0 + 0.6666666667

Combine like terms: 0 + 0.6666666667 = 0.6666666667
-7x + x2 = 0.6666666667

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 = 0.6666666667 + 12.25

Reorder the terms:
12.25 + -7x + x2 = 0.6666666667 + 12.25

Combine like terms: 0.6666666667 + 12.25 = 12.9166666667
12.25 + -7x + x2 = 12.9166666667

Factor a perfect square on the left side:
(x + -3.5)(x + -3.5) = 12.9166666667

Calculate the square root of the right side: 3.593976442

Break this problem into two subproblems by setting 
(x + -3.5) equal to 3.593976442 and -3.593976442.

Subproblem 1

x + -3.5 = 3.593976442 Simplifying x + -3.5 = 3.593976442 Reorder the terms: -3.5 + x = 3.593976442 Solving -3.5 + x = 3.593976442 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 = 3.593976442 + 3.5 Combine like terms: -3.5 + 3.5 = 0.0 0.0 + x = 3.593976442 + 3.5 x = 3.593976442 + 3.5 Combine like terms: 3.593976442 + 3.5 = 7.093976442 x = 7.093976442 Simplifying x = 7.093976442

Subproblem 2

x + -3.5 = -3.593976442 Simplifying x + -3.5 = -3.593976442 Reorder the terms: -3.5 + x = -3.593976442 Solving -3.5 + x = -3.593976442 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 = -3.593976442 + 3.5 Combine like terms: -3.5 + 3.5 = 0.0 0.0 + x = -3.593976442 + 3.5 x = -3.593976442 + 3.5 Combine like terms: -3.593976442 + 3.5 = -0.093976442 x = -0.093976442 Simplifying x = -0.093976442

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.093976442, -0.093976442}

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