a1=1/2=1/(1×2)a2=-1/6=-1/(2×3)a3=1/12=1/(3×4)a4=-1/20=-1/(4×5)a5=1/(5×6)=1/30a6=-1/(6×7)=-1/42a7=1/(7×8)=1/561/2,-1/6,1/12,-1/20,1/30,(-1/42),1/56答案为(-1/42)你如果采纳我,下次我还会帮助你...