1/2x3+1/3x4+1/4x5+.1/49x50
问题描述：
1/2x3+1/3x4+1/4x5+.1/49x50
答
1/2*3=(3-2)/2*3=3/2*3-2/2*3=1/2-1/31/3*4=(4-3)/3*4=4/3*4-3/3*4=1/3-1/4以此类推1/4*5=1/4-1/5……1/49*50=1/49-1/50所以1/2*3+1/3*4+……+1/49*50=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+……+(1/49-1/50)=1/2-1/50=12/...