Given the sequence 2, 6, 18, 54, ..., which expression shown would give the fifteenth term?
Every next term appears to be three times the previous term, so the sequence is defined recursively by
\(a_n=3a_{n-1}\)
and explicitly by
\(a_n=3a_{n-1}=3^2a_{n-2}=\cdots=3^{n-1}a_1\)
Given that \(a_1=2\), you have
\(a_n=2\times3^{n-1}\implies a_{15}=2\times3^{14}=9565938\)
Answer:
\(a_{15} = 2(3)^{14}\)
Step-by-step explanation:
the sequence 2, 6, 18, 54, ...,
3 is multiplied with first term to get 6
23 = 6
6 3= 18
18 * 3= 54
Each term is multiplied with 3 to get next term
Given sequence is geometric
To get nth term we use formula
\(a_n = a_1(r)^{n-1}\)
Where 'a1' is the first term
r is the common ratio
n is the number of terms
first term a1= 2
Each term is multiplied with 3 to get next term, so r= 3
now we need to find out the fifteenth term so n= 15
\(a_{15} = 2(3)^{15-1}\)
\(a_{15} = 2(3)^{14}\)