MathDB
Today's calculation of Integral 484

Source: 1983 Chiba University entrance exam

September 26, 2009
calculusintegrationlogarithmsgeometrylimittrapezoidcalculus computations

Problem Statement

Let C:y=lnxC: y=\ln x. For each positive integer nn, denote by AnA_n the area of the part enclosed by the line passing through two points (n, lnn), (n+1, ln(n+1))(n,\ \ln n),\ (n+1,\ \ln (n+1)) and denote by BnB_n that of the part enclosed by the tangent line at the point (n, lnn)(n,\ \ln n), CC and the line x=n+1x=n+1. Let g(x)=ln(x+1)lnxg(x)=\ln (x+1)-\ln x.
(1) Express An, BnA_n,\ B_n in terms of n, g(n)n,\ g(n) respectively.
(2) Find limnn{1ng(n)}\lim_{n\to\infty} n\{1-ng(n)\}.