(1/3+1/15+1/35+1/63+1/99+1/143)*80
问题描述:
(1/3+1/15+1/35+1/63+1/99+1/143)*80
答
(1/3+1/15+1/35+1/63+1/99+1/143)*80
=1/2*(1-1/3+1/3-1/5+1/5-1/7+.+1/11-1/13)*80
=40×【1-1/13】
=40×12/13
=480/13