College

Given the sequence:

\[ -2 \frac{2}{3}, -5 \frac{1}{3}, -10 \frac{2}{3}, -21 \frac{1}{3}, -42 \frac{2}{3}, \ldots \]

Which formula can be used to describe the sequence?

A. [tex]f(x+1) = -2 f(x)[/tex]

B. [tex]f(x+1) = -\frac{1}{2} f(x)[/tex]

C. [tex]f(x+1) = \frac{1}{2} f(x)[/tex]

D. [tex]f(x+1) = 2 f(x)[/tex]

Answer :

To find the formula that describes the given sequence, let's start by understanding the terms:

The sequence provided is:
- [tex]\(-2 \frac{2}{3}\)[/tex]
- [tex]\(-5 \frac{1}{3}\)[/tex]
- [tex]\(-10 \frac{2}{3}\)[/tex]
- [tex]\(-21 \frac{1}{3}\)[/tex]
- [tex]\(-42 \frac{2}{3}\)[/tex]

First, convert all mixed numbers to improper fractions to make the calculations easier:

1. [tex]\(-2 \frac{2}{3} = -\frac{8}{3}\)[/tex]
2. [tex]\(-5 \frac{1}{3} = -\frac{16}{3}\)[/tex]
3. [tex]\(-10 \frac{2}{3} = -\frac{32}{3}\)[/tex]
4. [tex]\(-21 \frac{1}{3} = -\frac{64}{3}\)[/tex]
5. [tex]\(-42 \frac{2}{3} = -\frac{128}{3}\)[/tex]

Next, let’s find the ratio between consecutive terms:

- The second term divided by the first term:
[tex]\[
\frac{-\frac{16}{3}}{-\frac{8}{3}} = 2
\][/tex]

- The third term divided by the second term:
[tex]\[
\frac{-\frac{32}{3}}{-\frac{16}{3}} = 2
\][/tex]

- The fourth term divided by the third term:
[tex]\[
\frac{-\frac{64}{3}}{-\frac{32}{3}} = 2
\][/tex]

- The fifth term divided by the fourth term:
[tex]\[
\frac{-\frac{128}{3}}{-\frac{64}{3}} = 2
\][/tex]

We can observe that the ratio between each pair of consecutive terms is consistently [tex]\(2\)[/tex]. This suggests the sequence is a geometric sequence with a common ratio of [tex]\(2\)[/tex].

This means the formula that describes the sequence is:

[tex]\[ f(x+1) = 2 \cdot f(x) \][/tex]

Therefore, the correct answer is: [tex]\( f(x+1) = 2 \cdot f(x) \)[/tex]