Posted by **j** on Tuesday, August 14, 2007 at 2:20am.

solve the system by addition:

-5x-9y = -5

x+5y=-15

I've tried this one over and over, but I can't seem to get the right answer. I don't even really know where to start. each time i try to do it, i go about it a little differently and i'm completely lost, pls help!!

from the second equation:

x=-5y-15

now sub that back in the first one:

-5(-5y-15)-9y=-5

25y+75-9y=-5

16y=-5-75

16y=-80

y=-5

now sub that back into x=-5y-15

x=-5(-5)-15

x=25-15

x=10

OR

first equation .....

-5x - 9y = -5

second equation times 5 ...

5x + 25y = -75

add them, the x's are eliminated

16y = -80

y = -5

substitute that in one of the originals, etc

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