=(1+1-1/2)+(1+1/2-1/3)+(1+1/3-1/4)+(1+1/4-1/5)+(1+1/5-1/6)+(1+1/6-1/7)
=6+(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)
=7-1/7
=48/7【附注】a/b表示b分之a