(13又1/13+12又1/12-11又1/11)/(13又1/13-10又1/11+11又1/12)
=(13又1/13+12又1/12-11又1/11)/(13又1/13-10又1/11-1+11又1/12+1)
=(13又1/13+12又1/12-11又1/11)/(13又1/13-11又1/11+12又1/12)
=1
(13又1/13+12又1/12-11又1/11)/(13又1/13-10又1/11+11又1/12)
=(13又1/13+12又1/12-11又1/11)/(13又1/13-10又1/11-1+11又1/12+1)
=(13又1/13+12又1/12-11又1/11)/(13又1/13-11又1/11+12又1/12)
=1