=1+1/3+1/6+1/10+1/15+1/21+1/28=1+1/2+(3十2)/30+1/7*(1/3+1/4)=1+1/2+1/6+1/7*7/12=1+2/3+1/12=1+(8+1)/12=1+3/4=1又3/4
