令bn=1/(an+1),则bn是等差数列,设公差为d
b3=b1+2d=1/3,b7=b1+6d=1/2
故d=1/24,b1=1/4
bn=1/24+(n-1)/4=(n+5)/24
即1/(an+1)=(n+5)/24
an=(19-n)/(n+5)
数列{an}中,a3=2,a7=1,且数列{1/(an+1)}是等差数列,则an=?
数列{an}中,a3=2,a7=1,且数列{1/(an+1)}是等差数列,则an=?
数学人气:585 ℃时间:2020-02-05 11:18:23
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