※ 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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