f(n)=3n^2-3n+1 求证1/f(1)+1/f(2)+1/f(3)+1/f(4)+1/f(5)+…+1/f(n)

题目

f(n)=3n^2-3n+1 求证1/f(1)+1/f(2)+1/f(3)+1/f(4)+1/f(5)+…+1/f(n)

答案

证明:
设g(n)=3n^2-3n
由于:f(n)=3n^2-3n+1>g(n)=3n^2-3n
则有：1/f(n)