10.18放狗

SeanH

一道数学：R是所有实数，I是整数，N是所有不是整数的实数。已知X+Y属于I，XY属于I，问Y是否属于N？
DS （1）X属于N
     （2）XY（X＋Y）属于I，且XY（X＋Y）是odd

Xrate

(1) only?

zkybq

楼主大好人~~~求多放放狗狗 逻辑阅读哇~~~

Xrate

不对不对， 应该是either is sufficient吧

passme

我猜D
Given: X+Y=integer, XY=integer
(1) X=Decimal. Sufficient because:
If X is decimal, then in order for X+Y = integer, Y  must be decimal.
(2) XY(X+Y) = integer, XY(X+Y) = odd, sufficient because:
in order for XY(X+Y) = odd, Both of XY and (X+Y) must be odd. Other wise Xy(X+Y）=even
now, in order for X+Y  AND XY to be odd at the same time, X or Y cannot be both odd And integers at the same time because of the following:
  odd+even=odd, but XY would be odd, violates (2). odd+odd =even, violates （2).
therefore, X and Y must be in decimal form===>N

素之菱雨

lz求逻辑狗~~~

木寻云

lz求阅读~~~

wangz52

求楼主回来~~