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