原式=1+1/3-7/12+9/20-11/30+13/42-15/56
=1+1/3-(7/3-7/4)+(9/4-9/5)-(11/5-11/6)+(13/6-13/7)-(15/7-15/8)
=1+(1/3-7/3)+(7/4+9/4)-(9/5+11/5)+(11/6+13/6)-(13/7+15/7)+15/8
=1-2+4-4+4-4+15/8
=-1+15/8
=7/8
原式=1+1/3-7/12+9/20-11/30+13/42-15/56
=1+1/3-(7/3-7/4)+(9/4-9/5)-(11/5-11/6)+(13/6-13/7)-(15/7-15/8)
=1+(1/3-7/3)+(7/4+9/4)-(9/5+11/5)+(11/6+13/6)-(13/7+15/7)+15/8
=1-2+4-4+4-4+15/8
=-1+15/8
=7/8