Chapter 8.3, Problem 23E

To determine

To write: the first five terms of the geometric sequence.

Answer to Problem 23E

The first five terms of the geometric sequence are $9,9e,9e^2,9e^3,9e^4$ .

Explanation of Solution

Given information:

The given sequence,

  $a_1=9,r=e$

Concept used:

The $n$ th term of geometric sequence has the form $a_1=a_1{r}^{n-1}$ where $r$ is the common ratio of the consecutive terms of the sequence.

Every geometric sequence can be written in the following form.

  $a_1=a_1,a_2=a_{1}r,a_3=a_1{r}^2,a_4=a_1{r}^3,\mathrm{...},a_n=a_1{r}^{n-1},\mathrm{..}$

Calculation:

The common ratio and the first term of the sequence is given

  $\begin{array}{l}{a}_1=9\\ r=e\end{array}$

To find the second term, multiply first term $e$ as shown below.

  $\begin{array}{c}{a}_2=a_1{r}^{2-1}\\ =9\left(e\right)\\ =9e\end{array}$

The 3^rd term can be calculated as

  $\begin{array}{c}{a}_3=a_1{r}^{3-1}\\ =9{\left(e\right)}^2\\ =9e^2\end{array}$

The 4^th term can be calculated as

  $\begin{array}{c}{a}_4=a_1{r}^{4-1}\\ =9{\left(e\right)}^3\\ =9e^3\end{array}$

The 5^th term can be calculated as

  $\begin{array}{c}{a}_5=a_1{r}^{5-1}\\ =9{\left(e\right)}^4\\ =9e^4\end{array}$

Hence, the first five terms of the geometric sequence are

  $9,9e,9e^2,9e^3,9e^4$ .