3x^2+21x-5.1=0

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Solution for 3x^2+21x-5.1=0 equation:


Simplifying
3x2 + 21x + -5.1 = 0

Reorder the terms:
-5.1 + 21x + 3x2 = 0

Solving
-5.1 + 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'.
-1.7 + 7x + x2 = 0

Move the constant term to the right:

Add '1.7' to each side of the equation.
-1.7 + 7x + 1.7 + x2 = 0 + 1.7

Reorder the terms:
-1.7 + 1.7 + 7x + x2 = 0 + 1.7

Combine like terms: -1.7 + 1.7 = 0.0
0.0 + 7x + x2 = 0 + 1.7
7x + x2 = 0 + 1.7

Combine like terms: 0 + 1.7 = 1.7
7x + x2 = 1.7

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 = 1.7 + 12.25

Reorder the terms:
12.25 + 7x + x2 = 1.7 + 12.25

Combine like terms: 1.7 + 12.25 = 13.95
12.25 + 7x + x2 = 13.95

Factor a perfect square on the left side:
(x + 3.5)(x + 3.5) = 13.95

Calculate the square root of the right side: 3.734969879

Break this problem into two subproblems by setting 
(x + 3.5) equal to 3.734969879 and -3.734969879.

Subproblem 1

x + 3.5 = 3.734969879 Simplifying x + 3.5 = 3.734969879 Reorder the terms: 3.5 + x = 3.734969879 Solving 3.5 + x = 3.734969879 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 = 3.734969879 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = 3.734969879 + -3.5 x = 3.734969879 + -3.5 Combine like terms: 3.734969879 + -3.5 = 0.234969879 x = 0.234969879 Simplifying x = 0.234969879

Subproblem 2

x + 3.5 = -3.734969879 Simplifying x + 3.5 = -3.734969879 Reorder the terms: 3.5 + x = -3.734969879 Solving 3.5 + x = -3.734969879 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 = -3.734969879 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = -3.734969879 + -3.5 x = -3.734969879 + -3.5 Combine like terms: -3.734969879 + -3.5 = -7.234969879 x = -7.234969879 Simplifying x = -7.234969879

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.234969879, -7.234969879}

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