2、原式 = lim(2-1/2^n) = 2-0 = 23、原式 = lim[(1-1/2)+(1/2-1/3)+.....+(1/n-1/(n+1))]=lim[1-1/(n+1)] = 1-0 = 1
u(n) = 1+1/2+1/4+...+1/2^n = (1-1/2^(n+1) ) /(1-1/2) = 2 - 1/2^nn->∞, 1/2^n ->0lim(n->∞) u(n) = 2
