1×2/1998+2×3/1998+3×4/1998+4×5/1998+5×6/1998
问题描述:
1×2/1998+2×3/1998+3×4/1998+4×5/1998+5×6/1998
答
1×2/1998+2×3/1998+3×4/1998+4×5/1998+5×6/1998 =1/1998×(1×2+2×3+3×4+4×5+5×6)=1/1998×[1*2+(2*3+3*4)+(4*5+5*6)]=1/1998×(2*1²+2*3²+2*5²)=1/1998×70=35/999...