使用列项相消法6*7*8=3365*6*7=2104*5*6=1203*4*5=602*3*4=241*2*3=61/(1*2*3)=(1/(1*2)-1/(2*3))/21/(2*3*4)=(1/(2*3)-1/(3*4))/2……原式=(1/(1*2)-1/(7*8))/2=(1/2-1/56)/2=7/112