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-4x+y=6
-5x-y=21
 Mar 29, 2014
 #1
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There are two ways to do this. This example is nice to just add the two equations (you could also subtract for similar problems)

-4x+y=6
+
-5x-y=21
-----------
-9x+0=27

---> x=-3

Then plug into one of the equations and solve for y

-4*(-3)+y=6

= 12+y=6

--> y=(-6)

You should then check the other equation is true

--> -5*(-3)-(-6)=21

= 15+6=21 which is true.

Alternatively you can simply solve for y in terms of x in the first equation ---> y=6+4x
then substitute this equation for y into the second equation where ever you see y (be careful with the negative signs), solve for x, and use that result to find y. I recommend doing it both ways to make sure you don't make any mistakes.

Hope this helps!
 Mar 29, 2014

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