5x^2-21x-12=0

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Solution for 5x^2-21x-12=0 equation:


Simplifying
5x2 + -21x + -12 = 0

Reorder the terms:
-12 + -21x + 5x2 = 0

Solving
-12 + -21x + 5x2 = 0

Solving for variable 'x'.

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

Divide each side by '5'.
-2.4 + -4.2x + x2 = 0

Move the constant term to the right:

Add '2.4' to each side of the equation.
-2.4 + -4.2x + 2.4 + x2 = 0 + 2.4

Reorder the terms:
-2.4 + 2.4 + -4.2x + x2 = 0 + 2.4

Combine like terms: -2.4 + 2.4 = 0.0
0.0 + -4.2x + x2 = 0 + 2.4
-4.2x + x2 = 0 + 2.4

Combine like terms: 0 + 2.4 = 2.4
-4.2x + x2 = 2.4

The x term is -4.2x.  Take half its coefficient (-2.1).
Square it (4.41) and add it to both sides.

Add '4.41' to each side of the equation.
-4.2x + 4.41 + x2 = 2.4 + 4.41

Reorder the terms:
4.41 + -4.2x + x2 = 2.4 + 4.41

Combine like terms: 2.4 + 4.41 = 6.81
4.41 + -4.2x + x2 = 6.81

Factor a perfect square on the left side:
(x + -2.1)(x + -2.1) = 6.81

Calculate the square root of the right side: 2.60959767

Break this problem into two subproblems by setting 
(x + -2.1) equal to 2.60959767 and -2.60959767.

Subproblem 1

x + -2.1 = 2.60959767 Simplifying x + -2.1 = 2.60959767 Reorder the terms: -2.1 + x = 2.60959767 Solving -2.1 + x = 2.60959767 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.1' to each side of the equation. -2.1 + 2.1 + x = 2.60959767 + 2.1 Combine like terms: -2.1 + 2.1 = 0.0 0.0 + x = 2.60959767 + 2.1 x = 2.60959767 + 2.1 Combine like terms: 2.60959767 + 2.1 = 4.70959767 x = 4.70959767 Simplifying x = 4.70959767

Subproblem 2

x + -2.1 = -2.60959767 Simplifying x + -2.1 = -2.60959767 Reorder the terms: -2.1 + x = -2.60959767 Solving -2.1 + x = -2.60959767 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.1' to each side of the equation. -2.1 + 2.1 + x = -2.60959767 + 2.1 Combine like terms: -2.1 + 2.1 = 0.0 0.0 + x = -2.60959767 + 2.1 x = -2.60959767 + 2.1 Combine like terms: -2.60959767 + 2.1 = -0.50959767 x = -0.50959767 Simplifying x = -0.50959767

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.70959767, -0.50959767}

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