Explain the pattern rule.

Question

a) -2,4,-8,16,-32
b) -15,30,90,-360

Answer 1

(a) each number is -2 times the previous
(b) I suspect a typo, since the signs do not alternate. However, a rule which works is that the nth term is n times the previous term, with sign changing when (n-1) is a multiple of 3.