5x^2-21x-72=0

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Solution for 5x^2-21x-72=0 equation:


Simplifying
5x2 + -21x + -72 = 0

Reorder the terms:
-72 + -21x + 5x2 = 0

Solving
-72 + -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'.
-14.4 + -4.2x + x2 = 0

Move the constant term to the right:

Add '14.4' to each side of the equation.
-14.4 + -4.2x + 14.4 + x2 = 0 + 14.4

Reorder the terms:
-14.4 + 14.4 + -4.2x + x2 = 0 + 14.4

Combine like terms: -14.4 + 14.4 = 0.0
0.0 + -4.2x + x2 = 0 + 14.4
-4.2x + x2 = 0 + 14.4

Combine like terms: 0 + 14.4 = 14.4
-4.2x + x2 = 14.4

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 = 14.4 + 4.41

Reorder the terms:
4.41 + -4.2x + x2 = 14.4 + 4.41

Combine like terms: 14.4 + 4.41 = 18.81
4.41 + -4.2x + x2 = 18.81

Factor a perfect square on the left side:
(x + -2.1)(x + -2.1) = 18.81

Calculate the square root of the right side: 4.337049688

Break this problem into two subproblems by setting 
(x + -2.1) equal to 4.337049688 and -4.337049688.

Subproblem 1

x + -2.1 = 4.337049688 Simplifying x + -2.1 = 4.337049688 Reorder the terms: -2.1 + x = 4.337049688 Solving -2.1 + x = 4.337049688 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 = 4.337049688 + 2.1 Combine like terms: -2.1 + 2.1 = 0.0 0.0 + x = 4.337049688 + 2.1 x = 4.337049688 + 2.1 Combine like terms: 4.337049688 + 2.1 = 6.437049688 x = 6.437049688 Simplifying x = 6.437049688

Subproblem 2

x + -2.1 = -4.337049688 Simplifying x + -2.1 = -4.337049688 Reorder the terms: -2.1 + x = -4.337049688 Solving -2.1 + x = -4.337049688 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 = -4.337049688 + 2.1 Combine like terms: -2.1 + 2.1 = 0.0 0.0 + x = -4.337049688 + 2.1 x = -4.337049688 + 2.1 Combine like terms: -4.337049688 + 2.1 = -2.237049688 x = -2.237049688 Simplifying x = -2.237049688

Solution

The solution to the problem is based on the solutions from the subproblems. x = {6.437049688, -2.237049688}

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