72=5x^2-4x-40

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Solution for 72=5x^2-4x-40 equation:


Simplifying
72 = 5x2 + -4x + -40

Reorder the terms:
72 = -40 + -4x + 5x2

Solving
72 = -40 + -4x + 5x2

Solving for variable 'x'.

Combine like terms: 72 + 40 = 112
112 + 4x + -5x2 = -40 + -4x + 5x2 + 40 + 4x + -5x2

Reorder the terms:
112 + 4x + -5x2 = -40 + 40 + -4x + 4x + 5x2 + -5x2

Combine like terms: -40 + 40 = 0
112 + 4x + -5x2 = 0 + -4x + 4x + 5x2 + -5x2
112 + 4x + -5x2 = -4x + 4x + 5x2 + -5x2

Combine like terms: -4x + 4x = 0
112 + 4x + -5x2 = 0 + 5x2 + -5x2
112 + 4x + -5x2 = 5x2 + -5x2

Combine like terms: 5x2 + -5x2 = 0
112 + 4x + -5x2 = 0

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

Divide each side by '-5'.
-22.4 + -0.8x + x2 = 0

Move the constant term to the right:

Add '22.4' to each side of the equation.
-22.4 + -0.8x + 22.4 + x2 = 0 + 22.4

Reorder the terms:
-22.4 + 22.4 + -0.8x + x2 = 0 + 22.4

Combine like terms: -22.4 + 22.4 = 0.0
0.0 + -0.8x + x2 = 0 + 22.4
-0.8x + x2 = 0 + 22.4

Combine like terms: 0 + 22.4 = 22.4
-0.8x + x2 = 22.4

The x term is -0.8x.  Take half its coefficient (-0.4).
Square it (0.16) and add it to both sides.

Add '0.16' to each side of the equation.
-0.8x + 0.16 + x2 = 22.4 + 0.16

Reorder the terms:
0.16 + -0.8x + x2 = 22.4 + 0.16

Combine like terms: 22.4 + 0.16 = 22.56
0.16 + -0.8x + x2 = 22.56

Factor a perfect square on the left side:
(x + -0.4)(x + -0.4) = 22.56

Calculate the square root of the right side: 4.749736835

Break this problem into two subproblems by setting 
(x + -0.4) equal to 4.749736835 and -4.749736835.

Subproblem 1

x + -0.4 = 4.749736835 Simplifying x + -0.4 = 4.749736835 Reorder the terms: -0.4 + x = 4.749736835 Solving -0.4 + x = 4.749736835 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.4' to each side of the equation. -0.4 + 0.4 + x = 4.749736835 + 0.4 Combine like terms: -0.4 + 0.4 = 0.0 0.0 + x = 4.749736835 + 0.4 x = 4.749736835 + 0.4 Combine like terms: 4.749736835 + 0.4 = 5.149736835 x = 5.149736835 Simplifying x = 5.149736835

Subproblem 2

x + -0.4 = -4.749736835 Simplifying x + -0.4 = -4.749736835 Reorder the terms: -0.4 + x = -4.749736835 Solving -0.4 + x = -4.749736835 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.4' to each side of the equation. -0.4 + 0.4 + x = -4.749736835 + 0.4 Combine like terms: -0.4 + 0.4 = 0.0 0.0 + x = -4.749736835 + 0.4 x = -4.749736835 + 0.4 Combine like terms: -4.749736835 + 0.4 = -4.349736835 x = -4.349736835 Simplifying x = -4.349736835

Solution

The solution to the problem is based on the solutions from the subproblems. x = {5.149736835, -4.349736835}

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