問題OG PS-Q379

[Ally]

PS.Q.379
An arithmetic sequence is a sequence in which eatch term after the first
is equal to the sum of numbers shown above is an arithmetic sequence,
which of the following must also be an arithmetic sequence?

I.2p,2r,2s,2t,2u
II.p-3,r-3,s-3,t-3,u-3
III.P的平方,r的平方,s的平方,t的平方,u的平方,

(A)I only
(B)IIonly
(c)IIIonly
(D)I and II
(E)II and III

看不懂題目 有沒有人可以幫幫我 :-S

[agk99]

其實不難，講的就是有一個數列，後面一個與前一個數差距是constant
你題目沒有完整喔

原數列是 p, r, s, t, u

就好比是3, 6, 9, 12, 15

結果乘以二倍，一定還是維持原數列的關係，全部都減3，也是不變
但要是通通平方，不就變成9, 36, 81, 144, 225,
原本關係就變了

所以選D