1*5/1+5*9/1+9*13/1+13*17/1+.45*49/1
问题描述：
1*5/1+5*9/1+9*13/1+13*17/1+.45*49/1
答
上面是分子吧,应该是这样写：
1/1*5+1/5*9+...+1/45*49
=1/4[1-1/5]+1/4[1/5-1/9]+...+1/4[1/45-1/49]
=1/4[1-1/5+1/5-1/9+...+1/45-1/49]
=1/4*[1-1/49]
=1/4*48/49
=12/49