(20-0.4x)(7-0.1x)=0

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Solution for (20-0.4x)(7-0.1x)=0 equation:


Simplifying
(20 + -0.4x)(7 + -0.1x) = 0

Multiply (20 + -0.4x) * (7 + -0.1x)
(20(7 + -0.1x) + -0.4x * (7 + -0.1x)) = 0
((7 * 20 + -0.1x * 20) + -0.4x * (7 + -0.1x)) = 0
((140 + -2x) + -0.4x * (7 + -0.1x)) = 0
(140 + -2x + (7 * -0.4x + -0.1x * -0.4x)) = 0
(140 + -2x + (-2.8x + 0.04x2)) = 0

Combine like terms: -2x + -2.8x = -4.8x
(140 + -4.8x + 0.04x2) = 0

Solving
140 + -4.8x + 0.04x2 = 0

Solving for variable 'x'.

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

Divide each side by '0.04'.
3500 + -120x + x2 = 0

Move the constant term to the right:

Add '-3500' to each side of the equation.
3500 + -120x + -3500 + x2 = 0 + -3500

Reorder the terms:
3500 + -3500 + -120x + x2 = 0 + -3500

Combine like terms: 3500 + -3500 = 0
0 + -120x + x2 = 0 + -3500
-120x + x2 = 0 + -3500

Combine like terms: 0 + -3500 = -3500
-120x + x2 = -3500

The x term is -120x.  Take half its coefficient (-60).
Square it (3600) and add it to both sides.

Add '3600' to each side of the equation.
-120x + 3600 + x2 = -3500 + 3600

Reorder the terms:
3600 + -120x + x2 = -3500 + 3600

Combine like terms: -3500 + 3600 = 100
3600 + -120x + x2 = 100

Factor a perfect square on the left side:
(x + -60)(x + -60) = 100

Calculate the square root of the right side: 10

Break this problem into two subproblems by setting 
(x + -60) equal to 10 and -10.

Subproblem 1

x + -60 = 10 Simplifying x + -60 = 10 Reorder the terms: -60 + x = 10 Solving -60 + x = 10 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '60' to each side of the equation. -60 + 60 + x = 10 + 60 Combine like terms: -60 + 60 = 0 0 + x = 10 + 60 x = 10 + 60 Combine like terms: 10 + 60 = 70 x = 70 Simplifying x = 70

Subproblem 2

x + -60 = -10 Simplifying x + -60 = -10 Reorder the terms: -60 + x = -10 Solving -60 + x = -10 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '60' to each side of the equation. -60 + 60 + x = -10 + 60 Combine like terms: -60 + 60 = 0 0 + x = -10 + 60 x = -10 + 60 Combine like terms: -10 + 60 = 50 x = 50 Simplifying x = 50

Solution

The solution to the problem is based on the solutions from the subproblems. x = {70, 50}

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