规律：1-1/3=1/3x2,1/3-1/5=1/3x1/5x2,1/5-1/7=1/5x1/7x2
问题描述：
规律：1-1/3=1/3x2,1/3-1/5=1/3x1/5x2,1/5-1/7=1/5x1/7x2
根据以上规律解答这道题
1x3/1+3x5/1+5x7/1+7x9/1+9x11/1+11x13/1+13x15/1+15x17/1+17x19/1+19x21/1
=
=
=
困惑死了 这上面给的规律和下面这题有上面关联请告诉我吧
答
1/1x3+1/3x5+1/5x7+1/7x9+1/9x11+1/11x13+1/13x15+1/15x17+1/17x19+1/19x21
=1/2x(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13+1/13-1/15+1/15-1/17+1/17-1/19+1/19-1/21)
=1/2x(1-1/21)
=1/2x20/21
=10/21