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Which formula can be used to find the [tex]$n$[/tex]th term of a geometric sequence where the first term is 8 and the common ratio is -3?

A. [tex]a_n = 8 \cdot (-3)^{n-1}[/tex]

B. [tex]a_n = -3 \cdot (8)^{n-1}[/tex]

C. [tex]a_n = (8 \cdot (-3))^{n-1}[/tex]

D. [tex]a_n = 8 \cdot (-3)^n[/tex]


Sagot :

To determine the correct formula for finding the [tex]\(n\)[/tex]th term of a geometric sequence, we need to follow these steps:

1. Identify the first term ([tex]\(a_1\)[/tex]): The first term of the sequence is given as 8.
2. Identify the common ratio ([tex]\(r\)[/tex]): The common ratio of this sequence is given as -3.
3. Recall the general formula for a geometric sequence: The general formula for the [tex]\(n\)[/tex]th term of a geometric sequence is given by:
[tex]\[ a_n = a_1 \cdot r^{n-1} \][/tex]

Now, substitute the given values into the general formula:

4. Substitute [tex]\(a_1 = 8\)[/tex] and [tex]\(r = -3\)[/tex] into the formula:
[tex]\[ a_n = 8 \cdot (-3)^{n-1} \][/tex]

By substituting the specific values for the first term and the common ratio into the general formula for the [tex]\(n\)[/tex]th term of a geometric sequence, we get:

[tex]\[ a_n = 8 \cdot (-3)^{n-1} \][/tex]

Thus, the correct formula to find the [tex]\(n\)[/tex]th term of this geometric sequence is:

[tex]\[ \boxed{a_n = 8 \cdot (-3)^{n-1}} \][/tex]
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