1/21+1/77+1/165.+1/3245 简便计算 请于22点前解答,
问题描述：
1/21+1/77+1/165.+1/3245 简便计算 请于22点前解答,
答
=1/4*(1/3-1/7)+1/4*(1/7-1/11)+………+1/4*(1/55-1/59)
=1/4*(1/3-1/7+1/7-1/11+...+1/55-1/59)
=1/4*(1/3-1/59)
=1/4*56/177
=14/177
答
1/21+1/77+1/165.+1/3245 =1/3*7+1/7*11+1/11*15.+1/55*59=1/4(1/3-1/7)+1/4(1/7-1/11)+1/4(1/11-1/15)+.1/4(1/55-1/59)=1/4(1/3-1/7+1/7-1/11.-1/59)=1/4(1/3-1/59)=1/4X56/177=14/177