Question 1082960
3rd term=12
4th term=8
Nth term=ar^n-1
  12=ar^2..i
   8=ar^3..ii
 divide through to eliminate a
3/2=r^-1
Solving i have
r=2/3
⇒12=ar^2..from i
 12=a*4/3
 a=27


 a=27
r=2/3
S∞=a/(1-r)
=81