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)=1/30
a6=-1/(6×7)=-1/42
a7=1/(7×8)=1/56
1/2,-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
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)=1/30
a6=-1/(6×7)=-1/42
a7=1/(7×8)=1/56
1/2,-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