1又1/3-8/15+12/35-16/63+20/99
=1+1/3-(1/3+1/5)+(1/5+1/7)-(1/7+1/9)+(1/9+1/11)
=1+1/3-1/3-1/5+1/5+1/7-1/7-1/9+1/9+1/11
=1+1/11
=1又1/11
1又1/3-8/15+12/35-16/63+20/99
=1+1/3-(1/3+1/5)+(1/5+1/7)-(1/7+1/9)+(1/9+1/11)
=1+1/3-1/3-1/5+1/5+1/7-1/7-1/9+1/9+1/11
=1+1/11
=1又1/11