The formula $20 - 2n$ defines the nth term of an arithmetic sequence where each term decreases by 2 as $n$ increases. Let's break down the task of finding the first three terms of this sequence by substituting $n = 1$, $n = 2$, and $n = 3$ into the nth term formula.

Step-by-Step Calculation:

1. For $n = 1$: $a_1 = 20 - 2(1) = 20 - 2 = 18$

2. For $n = 2$: $a_2 = 20 - 2(2) = 20 - 4 = 16$

3. For $n = 3$: $a_3 = 20 - 2(3) = 20 - 6 = 14$

First Three Terms

So, the first three terms of the sequence are: $18, 16, 14$

This sequence is an arithmetic sequence with a common difference of $-2$.

Would you like a deeper explanation or have additional questions?

Here are five questions that build on this sequence topic:

1. How do you find the common difference of an arithmetic sequence?
2. What will the 10th term of this sequence be?
3. How can you find the sum of the first 10 terms of this sequence?
4. How do you determine if a given number is a term in this sequence?
5. What happens to the sequence if the formula changes to $20 + 2n$?

Tip: In an arithmetic sequence, you can always check the common difference by subtracting any term from the term that follows it.