設(shè)級(jí)數(shù)un收斂,試判定下列級(jí)數(shù)的斂散性: un+1
計(jì)算下列對(duì)弧長的曲線積分:ds,其中Γ為曲線x=etcost,y=etsint,z=et上相應(yīng)于t從0變到2的這段弧.