12x^2-42x-20=0

Solution for 12x^2-42x-20=0 equation:

Simplifying
12x2 + -42x + -20 = 0

Reorder the terms:
-20 + -42x + 12x2 = 0

Solving
-20 + -42x + 12x2 = 0

Solving for variable 'x'.

Factor out the Greatest Common Factor (GCF), '2'.
2(-10 + -21x + 6x2) = 0

Ignore the factor 2.
Subproblem 1
Set the factor '(-10 + -21x + 6x2)' equal to zero and attempt to solve:

Simplifying
-10 + -21x + 6x2 = 0

Solving
-10 + -21x + 6x2 = 0

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

Divide each side by '6'.
-1.666666667 + -3.5x + x2 = 0

Move the constant term to the right:

Add '1.666666667' to each side of the equation.
-1.666666667 + -3.5x + 1.666666667 + x2 = 0 + 1.666666667

Reorder the terms:
-1.666666667 + 1.666666667 + -3.5x + x2 = 0 + 1.666666667

Combine like terms: -1.666666667 + 1.666666667 = 0.000000000
0.000000000 + -3.5x + x2 = 0 + 1.666666667
-3.5x + x2 = 0 + 1.666666667

Combine like terms: 0 + 1.666666667 = 1.666666667
-3.5x + x2 = 1.666666667

The x term is -3.5x.  Take half its coefficient (-1.75).
Square it (3.0625) and add it to both sides.

Add '3.0625' to each side of the equation.
-3.5x + 3.0625 + x2 = 1.666666667 + 3.0625

Reorder the terms:
3.0625 + -3.5x + x2 = 1.666666667 + 3.0625

Combine like terms: 1.666666667 + 3.0625 = 4.729166667
3.0625 + -3.5x + x2 = 4.729166667

Factor a perfect square on the left side:
(x + -1.75)(x + -1.75) = 4.729166667

Calculate the square root of the right side: 2.174664725

Break this problem into two subproblems by setting 
(x + -1.75) equal to 2.174664725 and -2.174664725.

Subproblem 1
x + -1.75 = 2.174664725

Simplifying
x + -1.75 = 2.174664725

Reorder the terms:
-1.75 + x = 2.174664725

Solving
-1.75 + x = 2.174664725

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '1.75' to each side of the equation.
-1.75 + 1.75 + x = 2.174664725 + 1.75

Combine like terms: -1.75 + 1.75 = 0.00
0.00 + x = 2.174664725 + 1.75
x = 2.174664725 + 1.75

Combine like terms: 2.174664725 + 1.75 = 3.924664725
x = 3.924664725

Simplifying
x = 3.924664725

Subproblem 2
x + -1.75 = -2.174664725

Simplifying
x + -1.75 = -2.174664725

Reorder the terms:
-1.75 + x = -2.174664725

Solving
-1.75 + x = -2.174664725

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '1.75' to each side of the equation.
-1.75 + 1.75 + x = -2.174664725 + 1.75

Combine like terms: -1.75 + 1.75 = 0.00
0.00 + x = -2.174664725 + 1.75
x = -2.174664725 + 1.75

Combine like terms: -2.174664725 + 1.75 = -0.424664725
x = -0.424664725

Simplifying
x = -0.424664725

Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {3.924664725, -0.424664725}
Solution
x = {3.924664725, -0.424664725}