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If (x,y) = (1,1) the above can be even.
if (x,y) = (2,2) the above is definitely even. So INSUFF!

2. (x+2)(y+2) = even
if (x,y) = (1,3) the eqn can be even
if (x,y) = (2,3) the eqn is still even. So INSUFF!

Combing both: Here comes the trouble (I don't have a neat approach)
O= odd
E = even
I came up with a truth table type apparoach

x y x(y+1) (x+2)(y+4)
O O True False
O E False True
E O True True
E E True True

So when x is odd, both (1) and (2) cannot be true at the same time. Hence x must be even. Hence C.

Sorry about my vague explanation, but this the best I could come up with.
_________________

"To dream anything that you want to dream, that is the beauty of the human mind. To do anything that you want to do, that is the strength of the human will. To trust yourself, to test your limits, that is the courage to succeed."

If (x,y) = (1,1) the above can be even. if (x,y) = (2,2) the above is definitely even. So INSUFF!

2. (x+2)(y+2) = even if (x,y) = (1,3) the eqn can be even if (x,y) = (2,3) the eqn is still even. So INSUFF!

Combing both: Here comes the trouble (I don't have a neat approach) O= odd E = even I came up with a truth table type apparoach

x y x(y+1) (x+2)(y+4) O O True False O E False True E O True True E E True True

So when x is odd, both (1) and (2) cannot be true at the same time. Hence x must be even. Hence C.

Sorry about my vague explanation, but this the best I could come up with.

The truth table way is interesting. It's amazing how you transform digital electronics to math

You got me here ywilfred! I am a Chip Design Engineer! I am gald you liked it.
_________________

"To dream anything that you want to dream, that is the beauty of the human mind. To do anything that you want to do, that is the strength of the human will. To trust yourself, to test your limits, that is the courage to succeed."