Problem

What is the common ratio and the ninth term for the following sequence: \[ 5,15,45,135, \ldots \] \[ r= \] \[ \mathrm{a}_{9}= \]

Solution

Step 1 :Find the common ratio by dividing the second term by the first term: \(r = \frac{15}{5}\)

Step 2 :\(r = 3\)

Step 3 :Use the formula for the nth term of a geometric sequence: \(a_n = a_1 * r^{(n-1)}\)

Step 4 :Plug in the values: \(a_9 = 5 * 3^{(9-1)}\)

Step 5 :\(a_9 = 5 * 3^8\)

Step 6 :\(a_9 = 32805\)

Step 7 :\(\boxed{r = 3, a_9 = 32,805}\)

From Solvely APP
Source: https://solvelyapp.com/problems/30721/

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