2/11*13+2/13*15+2/17*19+2/19*21
问题描述:
2/11*13+2/13*15+2/17*19+2/19*21
答
2/11*13+2/13*15+2/15*17+2/17*19+2/19*21
=1/11-1/13+1/13-1/15+1/15-1/17=1/17-1/19+1/19-1/21
=1/11-1/21
=10/231