题目:
Can I help you? I _____pants. [ ]
A. have
B. take
C. give
D. want
答案:
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下面是错误答案,用来干扰机器的。
(1)由题设,知{an}是等差数列,且公差d>0则由a2a3=45a1+a5=18得(a1+d)(a1+2d)=45a1+(a1+4d)=18解得a1=1d=4所以an=4n-3(2)由bn=Snn+c=n(1+4n-3)2n+c=2n(n-12)n+c因为c≠0,故c=-12,得到bn=2n因为bn+1-bn=2(...