How do you solve the following system?: 2x -5y =9 , 5x -3y = 2

1 Answer
Nov 18, 2015

y=-41/19color(white)(xxxx)x=-17/19

Keeping in fraction form improves precision

Explanation:

Given:
2x-5y=9..................................(1)
5x-3y=2..................................(2)

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color(blue)("Consider Equation (1)")

Add 5y to both sides
2x=9+5y

Subtract 9 from both sides.
2x-9 =5y

Divide both sides by 5
2/5 x-9/5 =y

Write in conventional form
color(green)(y=2/5x-9/5....................................(1_a))
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color(blue)("Consider Equation (2)")

Add 3y to both sides
5x=2+3y

Subtract 2 from both sides
5x-2=3y

Divide both sides by 3
5/3 x-2/3 = y

Write in conventional form
color(green)(y=5/3x-2/3....................................(2_a))
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To end up with just 1 variable thus solvable.

color(green)("Equation "(2_a))color(red)( =y= )color(blue)("Equation "(1_a)")

color(green)(2/5x-9/5) color(red)(=) color(blue)(5/3x-2/3)

Collecting like terms
2/5x -5/3x =9/5 -2/3

(6 -25)/15 x = (27 -10)/15

-19/15 x =17/15

-19x=17

color(red)(x=-17/19...........................(3))
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Substitute for x in Equation (1)

2x-5y=9..................................(1)

2color(red)((-17/19)) -5y=9

5y= 2(-17/19) -9

y= 2/5(-17/19)-9/5

color(red)(y=-2 3/19=-41/19...............(4))