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Home Q & A Board Science-Related Homework Help Mathematics
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rjlene rjlene
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11 years ago
solving by substitution what is the answer to 3x-y=17
                                                                               2x+5y=0
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wrote...
#1
11 years ago
3x-y=17
-y=17-3x
y=3x-17

2x+5y=0
2x+5(3x-17)=0
2x+15x-85=0
17x=85
x=5
plug back in to get y=-2
wrote...
#2
11 years ago
Ok, so lets start with 3x-y=17 and solve it for y:
3x-y=17
-y = 17-3x
y = 3x-17

Now, we use 2x+5y = 0. We have,
2x+5y = 0
since y = 3x-17 from before...
2x+5(3x-17) = 0
2x+15x-85=0
17x=85

x=5

Now, since y = 3x-17 from before...
y = 3(5)-17   Leftwards Arrow-- use x=5
y = -2

So the answer is y = -2, x = 5.
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