q=a4/a3=6/(-4)=-3/2
a2=a3/q=(-4)/(-3/2)=8/3
a1=a2/q=(8/3)/(-3/2)=-16/9
a5=a4q=6×(-3/2)=-9
S5=a1+a2+a3+a4+a5=-16/9+8/3-4+6-9=8/9-7=-55/9
q=a4/a3=6/(-4)=-3/2
a2=a3/q=(-4)/(-3/2)=8/3
a1=a2/q=(8/3)/(-3/2)=-16/9
a5=a4q=6×(-3/2)=-9
S5=a1+a2+a3+a4+a5=-16/9+8/3-4+6-9=8/9-7=-55/9