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Find the [tex]\(11^{\text{th}}\)[/tex] term of the sequence:
[tex]\[ 8, 24, 72, 216, \ldots \][/tex]

[tex]\(\boxed{\phantom{answer}}\)[/tex]


Sagot :

To find the [tex]$11^{\text{th}}$[/tex] term of the given sequence [tex]\(8, 24, 72, 216, \ldots\)[/tex], let's first understand the pattern of the sequence. This sequence is a geometric sequence.

In a geometric sequence, each term is obtained by multiplying the previous term with a constant ratio. Let's identify this ratio:
1. The first term is [tex]\(8\)[/tex].
2. To obtain the second term, we multiply the first term by the ratio [tex]\(r\)[/tex]:
[tex]\[ 8 \times r = 24 \][/tex]

Solving for [tex]\(r\)[/tex]:
[tex]\[ r = \frac{24}{8} = 3 \][/tex]

3. To confirm, we check this ratio for the next term:
[tex]\[ 24 \times 3 = 72 \][/tex]
[tex]\[ 72 \times 3 = 216 \][/tex]
So, the common ratio [tex]\(r\)[/tex] is [tex]\(3\)[/tex].

The general formula for the [tex]\(n\)[/tex]-th term of a geometric sequence is:
[tex]\[ a_n = a \times r^{n-1} \][/tex]
where [tex]\(a\)[/tex] is the first term, [tex]\(r\)[/tex] is the common ratio, and [tex]\(n\)[/tex] is the term number.

Given:
- [tex]\(a = 8\)[/tex]
- [tex]\(r = 3\)[/tex]
- [tex]\(n = 11\)[/tex]

We need to find the [tex]\(11^{\text{th}}\)[/tex] term ([tex]\(a_{11}\)[/tex]):
[tex]\[ a_{11} = 8 \times 3^{11-1} \][/tex]
[tex]\[ a_{11} = 8 \times 3^{10} \][/tex]

Thus, the [tex]$11^{\text{th}}$[/tex] term of the sequence is:
[tex]\[ 472392 \][/tex]

The [tex]$11^{\text{th}}$[/tex] term of the sequence is [tex]\( \boxed{472392} \)[/tex].