第1题错.第2题,易知,第91项是1/13,第92至100项是1/14,故和是13+9/14.=191/14.第1题,可设an=1+(n-1)d,bn=q^(n-1),由题设得,2d+1+q^4=21,4d+1+q^2=13.解得,d=q=2.故an=2d-1,bn=2^(n-1).
1.{an}是等差数列,{bn}是各项都为正数的等比数列,且a1=b1=1,a3+a5=21,a5+b3=13,求{an
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