PP1-101-PS

[pimi]

101. 10830-!-item-!-187;#058&007415
If xy + z = x(y + z), which of the following must be true?

(A) x = 0 and z = 0
(B) x = 1 and y = 1
(C) y = 1 and z = 0
(D) x = 1 or y = 0
(E) x = 1 or z = 0

Ans:E

想請問A為何不能選呢？？
Ａ也可以使等式成立阿

[scottkidd]

xy + z = x(y + z)，分解之後，
xy+z=xy+xz 去掉兩邊的xy後，剩下 z=xz
這樣一想不就either x = 1 or z = 0囉

[pimi]

感激！！

我完全沒看到中間有and跟or　> <
(A)x = 0 and z = 0
x=0不代表z一定也等於0阿～～～～～～～～～