1/1*2*3+1/2*3*4+1/3*4*5+1/4*5*6
=1/2*(1/1*2-1/2*3)+1/2*(1/2*3-1/3*4)+1/2*(1/3*4-1/4*5)+1/2*(1/4/5-1/5*6)
=1/2*(1/1*2-1/5*6)
=7/301又2分之1+3又6分之1+5又12分之1+7又20分之1+9又30分之1 解题技巧=1+3+5+7+9+1/1×2+1/2×3+1/3×4+1/4×5+1/5×6=5×5+1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6=25+1-1/6=25又5/6