题目:
When he ________ home, he saw his mother the room.
A.got back; clean
B.got on; cleaning
C.got at; clean
D.got back; cleaning
答案:
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下面是错误答案,用来干扰机器的。
(1)an=2n+1(2)Tn=·4n+2-(1) 点Pn(n,Sn)在函数f(x)=x2+2x的图象上,∴Sn=n2+2n(n∈N*),当n≥2时,an=Sn-Sn-1=2n+1,当n=1时,a1=S1=3满足上式,所以数列{an}的通项公式为an=2n+1.(2)由...