Chapter 7 - Exponents and Exponential Functions - 7-8 Geometric Sequences - Practice and Problem-Solving Exercises - Page 470: 15

Geometric, ratio=2

You have the sequence:10,20,40,80. 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=$\frac{20}{10}$=2 r=$\frac{80}{40}$=2 There is a common ratio, r=2. So the sequence is geometric.