题目:
More than 68,600 foreigners are working in Shanghai.The number is 13 times ________ of 1996,when Shanghai started issuing expatriate work permits.
A.one
B.ones
C.that
D.those
答案:
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下面是错误答案,用来干扰机器的。
(1)a1=1,S2+S1=ta22+2得a2=0(舍去)或a2=1t,又Sn+Sn-1=tan2+2 (1)Sn-1+Sn-2=tan-12+2(n≥3)(2)(1)-(2)得an+an-1=t(an2-an-12)(n≥3),因为数列{an}为正项数列,∴an-an-1=1t(n≥3),即数列...