x^2-7.2x-28=0

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Solution for x^2-7.2x-28=0 equation:


Simplifying
x2 + -7.2x + -28 = 0

Reorder the terms:
-28 + -7.2x + x2 = 0

Solving
-28 + -7.2x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '28' to each side of the equation.
-28 + -7.2x + 28 + x2 = 0 + 28

Reorder the terms:
-28 + 28 + -7.2x + x2 = 0 + 28

Combine like terms: -28 + 28 = 0
0 + -7.2x + x2 = 0 + 28
-7.2x + x2 = 0 + 28

Combine like terms: 0 + 28 = 28
-7.2x + x2 = 28

The x term is -7.2x.  Take half its coefficient (-3.6).
Square it (12.96) and add it to both sides.

Add '12.96' to each side of the equation.
-7.2x + 12.96 + x2 = 28 + 12.96

Reorder the terms:
12.96 + -7.2x + x2 = 28 + 12.96

Combine like terms: 28 + 12.96 = 40.96
12.96 + -7.2x + x2 = 40.96

Factor a perfect square on the left side:
(x + -3.6)(x + -3.6) = 40.96

Calculate the square root of the right side: 6.4

Break this problem into two subproblems by setting 
(x + -3.6) equal to 6.4 and -6.4.

Subproblem 1

x + -3.6 = 6.4 Simplifying x + -3.6 = 6.4 Reorder the terms: -3.6 + x = 6.4 Solving -3.6 + x = 6.4 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.6' to each side of the equation. -3.6 + 3.6 + x = 6.4 + 3.6 Combine like terms: -3.6 + 3.6 = 0.0 0.0 + x = 6.4 + 3.6 x = 6.4 + 3.6 Combine like terms: 6.4 + 3.6 = 10 x = 10 Simplifying x = 10

Subproblem 2

x + -3.6 = -6.4 Simplifying x + -3.6 = -6.4 Reorder the terms: -3.6 + x = -6.4 Solving -3.6 + x = -6.4 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.6' to each side of the equation. -3.6 + 3.6 + x = -6.4 + 3.6 Combine like terms: -3.6 + 3.6 = 0.0 0.0 + x = -6.4 + 3.6 x = -6.4 + 3.6 Combine like terms: -6.4 + 3.6 = -2.8 x = -2.8 Simplifying x = -2.8

Solution

The solution to the problem is based on the solutions from the subproblems. x = {10, -2.8}

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