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by truplayer256 » Sun Oct 11, 2009 8:17 pm
If x + |x| + y = 7 and x + |y| - y =6 , then x + y =

x+|x|+y=7

x+|y|-y=6

|x|=7-y-x

x could equal 7-y-x or -(7-y-x)

x=7-y-x-->x=(7-y)/2

x=-7+y+x--> 0=-7+y. This really isn't useful at all.

Substitute the x=(7-y)/2 into the second equation to obtain y=-1 or y=7.

From this we get x=4 or x=0.

x+y=4-1=3 or 0+7=7.
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by sanjana » Sun Oct 11, 2009 10:29 pm
What were the Answer choices give?
What it 7 and 3 were part of the answers.
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by bullzeye » Mon Oct 12, 2009 4:59 am
If we substitute what trueplayer has found for x and y in the original equation we'll see that the answer is:

x=4 and y=-1 only.

But I was really hoping for an easier method...
I couldn't find one myself, unfortunately...
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