gwd 18 36

Q36:

If x and y are integers, is y an even integer?

(1)   2y – x = x² – y²

(2)   x is an odd integer.

选C, 由2个条件可以推出Y 是 偶数

y^2+2y=x+x^2

(y+1)^2=x^2+x+1

x odd,-----> x^2+x+1  odd,-----> y+1 odd---->y even

x even----->x^2+x+1  odd,------------------->y even

answer:A

支持A

GG们都好厉害啊!

谢谢

(1)   2y – x = x² – y²   

       ^{x(x+1)=y(y+2), the left side must be even, then y must be even , A is sufficient}

同意A,PFPF