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