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May 24, 2015

Homework Help: alg.

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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