来自黄兴的问题
1/3*5+1/5*7+1/7*9+1/9*11+1/11*13+1/13*15=?
1/3*5+1/5*7+1/7*9+1/9*11+1/11*13+1/13*15=?
1回答
2020-09-2700:39
1/3*5+1/5*7+1/7*9+1/9*11+1/11*13+1/13*15=?
1/3*5+1/5*7+1/7*9+1/9*11+1/11*13+1/13*15=?
原式=1/3*5+1/5*7+1/7*9+1/9*11+1/11*13+1/13*15
=1/2(1/3-1/5+1/5-1/7+.+1/11-1/13+1/13-1/15)
=1/2(1/3-1/15)
=1/2*4/15
=2/15.