把等式化简
得
4*Q=2+D
Q^2*(2+2D)=3
得Q约=0.83
D=1.32
an=1.32*n-0.32
bn=2*0.83^(n-1)
n=52 abn=0.0102
n=53 abn=0.008629
所以N=53
an等比,bn等差,a1=1,b1=2,a3b3=3,b2=4a2,求当abn
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