Question

等比数列{an}的首项为a1=a,公比不等于1,则1/a1a2+1/a2a3+...+1/ana(n+1)=?

Answer 1

=1/a1^2(1/q+1/q^3+1/q^5+1/q^7+...+1/q^(2n-1))

=1/a^2*1/q*(1-1/q^2n)/(1-q)