3x^2+21x-6.9=0

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Solution for 3x^2+21x-6.9=0 equation:


Simplifying
3x2 + 21x + -6.9 = 0

Reorder the terms:
-6.9 + 21x + 3x2 = 0

Solving
-6.9 + 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'.
-2.3 + 7x + x2 = 0

Move the constant term to the right:

Add '2.3' to each side of the equation.
-2.3 + 7x + 2.3 + x2 = 0 + 2.3

Reorder the terms:
-2.3 + 2.3 + 7x + x2 = 0 + 2.3

Combine like terms: -2.3 + 2.3 = 0.0
0.0 + 7x + x2 = 0 + 2.3
7x + x2 = 0 + 2.3

Combine like terms: 0 + 2.3 = 2.3
7x + x2 = 2.3

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 = 2.3 + 12.25

Reorder the terms:
12.25 + 7x + x2 = 2.3 + 12.25

Combine like terms: 2.3 + 12.25 = 14.55
12.25 + 7x + x2 = 14.55

Factor a perfect square on the left side:
(x + 3.5)(x + 3.5) = 14.55

Calculate the square root of the right side: 3.814446225

Break this problem into two subproblems by setting 
(x + 3.5) equal to 3.814446225 and -3.814446225.

Subproblem 1

x + 3.5 = 3.814446225 Simplifying x + 3.5 = 3.814446225 Reorder the terms: 3.5 + x = 3.814446225 Solving 3.5 + x = 3.814446225 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 = 3.814446225 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = 3.814446225 + -3.5 x = 3.814446225 + -3.5 Combine like terms: 3.814446225 + -3.5 = 0.314446225 x = 0.314446225 Simplifying x = 0.314446225

Subproblem 2

x + 3.5 = -3.814446225 Simplifying x + 3.5 = -3.814446225 Reorder the terms: 3.5 + x = -3.814446225 Solving 3.5 + x = -3.814446225 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 = -3.814446225 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = -3.814446225 + -3.5 x = -3.814446225 + -3.5 Combine like terms: -3.814446225 + -3.5 = -7.314446225 x = -7.314446225 Simplifying x = -7.314446225

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.314446225, -7.314446225}

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