A set of numbers has the property that for any number t in the set, t + 2 is in the set. If –1 is in the set, which of the following must also be in the set?
I. -3
II. 1
III. 5
A. I only
B. II only
C. I and II only
D. II and III only
E. I, II, and III
請問III為什麼可以?I為什麼不符合?我在算的時候是認為-1=t那t+2=1符合,or t+2=-1,t=-3也對.但答案是II&III對.
請問這要怎麼解?謝謝!
p.s.另外我想請問,我對了精華區的題號gwd1-10的討論和我這題題目不一樣耶,是因為gwd版本不同嗎?我的是標題寫gwd 31套的那個~這要怎麼分辨?謝謝!
