Answer:
-3
Step-by-step explanation:
an = a1·r^(n-1) . . . . . . general term of a geometric sequence
a5 = 324 = 4·r(5-1) . . . specifically, the 5th term
81 = r^4 . . . . . . . . . . . divide by 4
Since the sum of 5 terms is less than the 5th term, the value of r must be negative:
[tex]r=-\sqrt[4]{81}=-3[/tex]
