已知1/3-1/5=2/15;1/5-1/7=2/35… 求1/15+1/35+1/63+1/99

问题描述:

已知1/3-1/5=2/15;1/5-1/7=2/35… 求1/15+1/35+1/63+1/99

1/15+1/35+1/63+1/99
=1/2*(1/3-1/5)+1/2*(1/5-1/7)+1/2*(1/7-1/9)+1/2*(1/9-1/11)
=1/2*(1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)
=1/2*(1/3-1/11)
=1/2*(11/33-3/33)
=1/2*8/33
=4/33