巧算 /为分数线 1/3+1/15+1/35+1/63+1/99
问题描述:
巧算 /为分数线 1/3+1/15+1/35+1/63+1/99
答
1/3+1/15+1/35+1/63+1/99 =1/2(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)
=1/2(1-1/11)=1/2×10/11=5/11