pp T2-DS 39

[gman]

39.If c and d are integers, is c even?

(1) c(d + 1) is even.

(2) (c + 2)(d + 4) is even

ans : C

我選 E

1,2 兩個都 insuficient 怎麼推到 C呢? 我的數學阿

[mupeane]

設正為+，負為-
(1) c(d + 1) is even.

(C, D)=(+, +) or (-, -) or (+, -)

(2) (c + 2)(d + 4) is even

(C, D)=(+, +) or (+, -) or (-, +)

由(1)跟(2)可得

(C, D)=(+, +) or (+, -)
所以C為偶數

[gman]

太感謝了!!!

[caneton]

應該是偶數設+ 奇數設-

可能打太快嚕~呵呵~

真是好方法呢~感謝