Evaluating Exponential Functions

Let $f (x) = 5 {(3)}^{x + 1} .$ Evaluate $f (2)$ without using a calculator.

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Solution
Follow the order of operations. Be sure to pay attention to the parentheses.

$\begin{array}{l} f (x) & = 5 {(3)}^{x + 1} \\ f (2) & = 5 {(3)}^{2 + 1} & Substitute x = 2. \\ = 5 {(3)}^{3} & Add the exponents . \\ = 5 (27) & Simplify the power . \\ = 135 & Multiply . \end{array}$

Your turn

The book's Try It right after this example: same idea, new numbers. Only the answer is given.

Let $f (x) = 8 {(1.2)}^{x - 5} .$ Evaluate $f (3)$ using a calculator. Round to four decimal places.

How did it go?