8.
1 answer:
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Answer:
2/3
Step-by-step explanation:
Let's define z = x-y, so solving for z will tell us exactly what we want to know. Then we can substitute for x: x = z+y, and our equations become ...
7(z+y)+3y = 8 ⇒ 7z +10y = 8
6(z+y)-3y = 5 ⇒ 6z +3y = 5
We can eliminate the y-variable by subtracting 3 times the first equation from 10 times the second:
10(6z +3y) -3(7z +10y) = 10(5) -3(8)
60z +30y -21z -30y = 50 -24 . . . . eliminate parentheses
39z = 26 . . . . collect terms
z = 26/39 = 2/3 . . . . . divide by the coefficient of z and reduce
The value of x - y is 2/3.
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The attached graph shows (x, y) = (1, 1/3), so x - y = 1 - 1/3 = 2/3.
