Antara
Last Activity: 3 Years ago
51.f(r,n)=n-n^2{nn(1+1/n)(1+1/rn)(1+1/r2n).......}n. (Taking n common from each bracket)
= n-n^2 . nn^2 {1+1/n)(1+1/rn).....}n
Taking log both sides,
ln(f(r,n))=n{ln(1+1/n)+ln(1+1/rn)+ln(1+1/r2n)+......}
Taking lim n->inf both sides
RHS=lim(n->inf) {nln(1+1/n)+nln(1+1/rn)+nln(1+1/r2n)+.......}
Now lim(n->inf) n *ln(1+1/n) (inf*0 form of limit)
= lim(n->inf)
=lim(n->inf)
…............(L hospital rule)
= 1
similarly second term=1/r , 3rd term=1/r^2 and so on
so ques 51. ans =e(1+1/r+1/r^2+1/r^3+.......inf)=e3/2 (Putting r=3 and applying sum of inf GP formula)