※ 引述《Jinai (橘子汽水好喝~)》之銘言：
: 167
: If x, y, and z are integers and xy + z is an odd integer, is x an even integer?
: (1) xy + xz is an even integer.
: (2) y + xz is an odd integer.
: ans:(A)
條件式: xy+z = odd
與(1)相減 : (x-1)z = even - odd = odd
又odd 必為 odd * odd => x-1 為odd , 且z為odd
故由(1)即可知 x為even
但與(2)相減 : (x-1)(y-z) = odd - odd 為even
無法得知 x-1為 odd or even
故選(a)
我也不知道對不對@@"
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