Answer:
[tex]f(n) = \frac{32}{3}(\frac{3}{2})^n[/tex]
Step-by-step explanation:
Given
[tex]r = \frac{3}{2}[/tex]
[tex]f(5) = 81[/tex]
Required
The geometric sequence
A geometric sequence is represented as:
[tex]f(n) = ar^{n-1}[/tex]
Replace n with 5
[tex]f(5) = ar^{5-1}[/tex]
[tex]f(5) = ar^4[/tex]
Substitute values for f(5) and r
[tex]81 = a* (\frac{3}{2})^4[/tex]
Open bracket
[tex]81 = a* \frac{81}{16}[/tex]
Make a the subject
[tex]a = \frac{81 * 16}{81}[/tex]
[tex]a = 16[/tex]
So, the explicit function is:
[tex]f(n) = ar^{n-1}[/tex]
[tex]f(n) = 16 * (\frac{3}{2})^{n-1}[/tex]
Split
[tex]f(n) = 16 * (\frac{3}{2})^n \div (\frac{3}{2})[/tex]
Convert to multiplication
[tex]f(n) = 16 * (\frac{3}{2})^n * \frac{2}{3}[/tex]
[tex]f(n) = \frac{32}{3}(\frac{3}{2})^n[/tex]
