Chapter 7 - Exponents and Exponential Functions - 7-8 Geometric Sequences - Practice and Problem-Solving Exercises - Page 470: 19

Geometric,the common ratio is 4.

You have the sequence:81,27,9,3. Find the common ratio by using the formula: R=$\frac{a2}{a1}$,R=$\frac{a4}{a3}$.Plug in the values to get the ratios. r=$\frac{20}{5}$=4 r=$\frac{320}{80}$=4 There is a common ratio, r=4. So the sequence is geometric.