Mathematics for IGCSE & O level - Sequences (Section 2 - No. 37)

Given the sequence 11, 7, 3, -1, ..., what is the nth term?

-4n + 15

4n - 15

4n + 7

-4n -11

The difference is -4 each time, so it includes -4n. When n = 1, the term is 11, thus -4(1) + 15 = 11, therefore, the formula is -4n + 15.