1st question of lunchtime

Can anyone please explain the 1st question? I know its easy, but still I couldnt do.

The only thing you have to do is, out of X, Y and Z, if the sum of any two numbers is equal to the third number, print “yes”, else print “no”. If you’re unable to think why this is so, read the editorial.

I check only for all possibilites and observe that Only i have to do is to check three conditions
x+y==z
y+z==x
x+z==y
It all I have Done

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