3. In an arithmetic sequence the 7th term is 21 and the common difference is -6. Find the first term and the 11th term.
| Solution: | |
| Using the formula nth term = a + (n-1)d | |
| = a + x -6 | |
| = a + | |
| = a | |
| Therefore, the first term is | |
| The 11th term is + (11 - 1) = | |
|
|