数学jj242

julia_juer

DS 题 问xy是否是even number， 条件1，x+y 是 even number 条件2 x^2+xy+y^2是even number

aeolusero二

1, not sufficient

x=1, y=3, xy=3 or x=2, y=4, xy=8

2. = (x+Y)^2 - xy   again depends on X+y is even or not, not

sufficient

but togther are sufficient

myungryong

这题选B吧 (x+y)^2 -xy = even
奇数-奇数=偶 xy是奇数的时候x和y必须都是奇数 奇数之和又为偶数 所以(x+y)^2必是偶数 矛盾
所以xy必是偶数
B

f2050711489

the answer should be "B"