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What is the common ratio of the following geometric sequence?

[tex]\[6, 15, \frac{75}{2}, \frac{375}{4}, \ldots\][/tex]

A. [tex]\( r = \frac{5}{2} \)[/tex]
B. [tex]\( r = \frac{2}{5} \)[/tex]
C. [tex]\( r = 2 \)[/tex]
D. [tex]\( r = -2 \)[/tex]


Sagot :

To determine the common ratio of the given geometric sequence [tex]\(6, 15, \frac{75}{2}, \frac{375}{4}, \ldots\)[/tex], we follow these steps:

1. Identify the first few terms of the sequence:
- The first term [tex]\(a_1\)[/tex] is [tex]\(6\)[/tex].
- The second term [tex]\(a_2\)[/tex] is [tex]\(15\)[/tex].
- The third term [tex]\(a_3\)[/tex] is [tex]\(\frac{75}{2}\)[/tex].
- The fourth term [tex]\(a_4\)[/tex] is [tex]\(\frac{375}{4}\)[/tex].

2. The common ratio [tex]\(r\)[/tex] in a geometric sequence is calculated by dividing any term by its preceding term. We calculate the common ratio between each pair of successive terms:

- For [tex]\(a_2\)[/tex] and [tex]\(a_1\)[/tex]:
[tex]\[ r = \frac{a_2}{a_1} = \frac{15}{6} = 2.5 \][/tex]

- For [tex]\(a_3\)[/tex] and [tex]\(a_2\)[/tex]:
[tex]\[ r = \frac{a_3}{a_2} = \frac{\frac{75}{2}}{15} = \frac{75}{2 \times 15} = \frac{75}{30} = 2.5 \][/tex]

- For [tex]\(a_4\)[/tex] and [tex]\(a_3\)[/tex]:
[tex]\[ r = \frac{a_4}{a_3} = \frac{\frac{375}{4}}{\frac{75}{2}} = \frac{375 \times 2}{4 \times 75} = \frac{750}{300} = 2.5 \][/tex]

3. Since the common ratio [tex]\(r\)[/tex] is consistent between each pair of successive terms and equals [tex]\(2.5\)[/tex], we conclude that the common ratio of the given geometric sequence is:
[tex]\[ r = 2.5 \][/tex]

Thus, the option [tex]\( r = \frac{5}{2} \)[/tex] matches the calculated common ratio.