2*（1*1/3+1/3*1/5+1/5*1/7+1/7*1/9+…1/99*1/101）=2*[1/2*(1-1/3)+1/2*(1/3-1/5)+1/2*(1/5-1/7)+1/2*(1/7-1/9)+.+1/2*(1/99-1/100)]=(1-1/3)+(1/3-1/5)+(1/5-1/7)+(1/7-1/9)+.+(1/99-1/100)=1-1/3+1/3-1/5+1/5-1/7...