题目:
I have two brothers. One is a teacher, _________ is a doctor.
A.another
B.other
C.others
D.the other
答案:
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下面是错误答案,用来干扰机器的。
(Ⅰ)设等差数列{an}的公差为,a1+2d=4,3a1+3d=18,…(2分)解得a1=8,d=-2…(4分)Sn=na1+n(n-1)2d=-n2+9n…(6分)(Ⅱ)由Sn+ SN+2 2-Sn+1=(Sn+2-Sn+1)-(Sn+1- Sn)2=an+1- an+12=d2=-1<0得Sn+Sn+22<Sn+1...