(2x-5)(x+4)-20=0

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Solution for (2x-5)(x+4)-20=0 equation:


Simplifying
(2x + -5)(x + 4) + -20 = 0

Reorder the terms:
(-5 + 2x)(x + 4) + -20 = 0

Reorder the terms:
(-5 + 2x)(4 + x) + -20 = 0

Multiply (-5 + 2x) * (4 + x)
(-5(4 + x) + 2x * (4 + x)) + -20 = 0
((4 * -5 + x * -5) + 2x * (4 + x)) + -20 = 0
((-20 + -5x) + 2x * (4 + x)) + -20 = 0
(-20 + -5x + (4 * 2x + x * 2x)) + -20 = 0
(-20 + -5x + (8x + 2x2)) + -20 = 0

Combine like terms: -5x + 8x = 3x
(-20 + 3x + 2x2) + -20 = 0

Reorder the terms:
-20 + -20 + 3x + 2x2 = 0

Combine like terms: -20 + -20 = -40
-40 + 3x + 2x2 = 0

Solving
-40 + 3x + 2x2 = 0

Solving for variable 'x'.

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

Divide each side by '2'.
-20 + 1.5x + x2 = 0

Move the constant term to the right:

Add '20' to each side of the equation.
-20 + 1.5x + 20 + x2 = 0 + 20

Reorder the terms:
-20 + 20 + 1.5x + x2 = 0 + 20

Combine like terms: -20 + 20 = 0
0 + 1.5x + x2 = 0 + 20
1.5x + x2 = 0 + 20

Combine like terms: 0 + 20 = 20
1.5x + x2 = 20

The x term is 1.5x.  Take half its coefficient (0.75).
Square it (0.5625) and add it to both sides.

Add '0.5625' to each side of the equation.
1.5x + 0.5625 + x2 = 20 + 0.5625

Reorder the terms:
0.5625 + 1.5x + x2 = 20 + 0.5625

Combine like terms: 20 + 0.5625 = 20.5625
0.5625 + 1.5x + x2 = 20.5625

Factor a perfect square on the left side:
(x + 0.75)(x + 0.75) = 20.5625

Calculate the square root of the right side: 4.534589287

Break this problem into two subproblems by setting 
(x + 0.75) equal to 4.534589287 and -4.534589287.

Subproblem 1

x + 0.75 = 4.534589287 Simplifying x + 0.75 = 4.534589287 Reorder the terms: 0.75 + x = 4.534589287 Solving 0.75 + x = 4.534589287 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.75' to each side of the equation. 0.75 + -0.75 + x = 4.534589287 + -0.75 Combine like terms: 0.75 + -0.75 = 0.00 0.00 + x = 4.534589287 + -0.75 x = 4.534589287 + -0.75 Combine like terms: 4.534589287 + -0.75 = 3.784589287 x = 3.784589287 Simplifying x = 3.784589287

Subproblem 2

x + 0.75 = -4.534589287 Simplifying x + 0.75 = -4.534589287 Reorder the terms: 0.75 + x = -4.534589287 Solving 0.75 + x = -4.534589287 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.75' to each side of the equation. 0.75 + -0.75 + x = -4.534589287 + -0.75 Combine like terms: 0.75 + -0.75 = 0.00 0.00 + x = -4.534589287 + -0.75 x = -4.534589287 + -0.75 Combine like terms: -4.534589287 + -0.75 = -5.284589287 x = -5.284589287 Simplifying x = -5.284589287

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.784589287, -5.284589287}

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