2/11×13+2/13×15+2/17×19+2/19*21+1/21 怎么简便!

问题描述:

2/11×13+2/13×15+2/17×19+2/19*21+1/21 怎么简便!

2/11×13+2/13×15+2/17×19+2/19*21+1/21
=1/11-1/13+1/13-1/15+1/15-1/17-1/17-1/19+1/19-1/21+1/21
=1/11
如果本题有什么不明白可以追问,