0=5x^2-28x-80

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Solution for 0=5x^2-28x-80 equation:


Simplifying
0 = 5x2 + -28x + -80

Reorder the terms:
0 = -80 + -28x + 5x2

Solving
0 = -80 + -28x + 5x2

Solving for variable 'x'.

Combine like terms: 0 + 80 = 80
80 + 28x + -5x2 = -80 + -28x + 5x2 + 80 + 28x + -5x2

Reorder the terms:
80 + 28x + -5x2 = -80 + 80 + -28x + 28x + 5x2 + -5x2

Combine like terms: -80 + 80 = 0
80 + 28x + -5x2 = 0 + -28x + 28x + 5x2 + -5x2
80 + 28x + -5x2 = -28x + 28x + 5x2 + -5x2

Combine like terms: -28x + 28x = 0
80 + 28x + -5x2 = 0 + 5x2 + -5x2
80 + 28x + -5x2 = 5x2 + -5x2

Combine like terms: 5x2 + -5x2 = 0
80 + 28x + -5x2 = 0

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

Divide each side by '-5'.
-16 + -5.6x + x2 = 0

Move the constant term to the right:

Add '16' to each side of the equation.
-16 + -5.6x + 16 + x2 = 0 + 16

Reorder the terms:
-16 + 16 + -5.6x + x2 = 0 + 16

Combine like terms: -16 + 16 = 0
0 + -5.6x + x2 = 0 + 16
-5.6x + x2 = 0 + 16

Combine like terms: 0 + 16 = 16
-5.6x + x2 = 16

The x term is -5.6x.  Take half its coefficient (-2.8).
Square it (7.84) and add it to both sides.

Add '7.84' to each side of the equation.
-5.6x + 7.84 + x2 = 16 + 7.84

Reorder the terms:
7.84 + -5.6x + x2 = 16 + 7.84

Combine like terms: 16 + 7.84 = 23.84
7.84 + -5.6x + x2 = 23.84

Factor a perfect square on the left side:
(x + -2.8)(x + -2.8) = 23.84

Calculate the square root of the right side: 4.882622246

Break this problem into two subproblems by setting 
(x + -2.8) equal to 4.882622246 and -4.882622246.

Subproblem 1

x + -2.8 = 4.882622246 Simplifying x + -2.8 = 4.882622246 Reorder the terms: -2.8 + x = 4.882622246 Solving -2.8 + x = 4.882622246 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.8' to each side of the equation. -2.8 + 2.8 + x = 4.882622246 + 2.8 Combine like terms: -2.8 + 2.8 = 0.0 0.0 + x = 4.882622246 + 2.8 x = 4.882622246 + 2.8 Combine like terms: 4.882622246 + 2.8 = 7.682622246 x = 7.682622246 Simplifying x = 7.682622246

Subproblem 2

x + -2.8 = -4.882622246 Simplifying x + -2.8 = -4.882622246 Reorder the terms: -2.8 + x = -4.882622246 Solving -2.8 + x = -4.882622246 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.8' to each side of the equation. -2.8 + 2.8 + x = -4.882622246 + 2.8 Combine like terms: -2.8 + 2.8 = 0.0 0.0 + x = -4.882622246 + 2.8 x = -4.882622246 + 2.8 Combine like terms: -4.882622246 + 2.8 = -2.082622246 x = -2.082622246 Simplifying x = -2.082622246

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.682622246, -2.082622246}

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