If the fourth term in a geometric sequence is –1 and the common ratio is –1, find the explicit formula of the sequence.
Question 15 options:

A)

an = (1) ⋅ (–1)n – 1 for n ≥ 1

B)

an = (– 1) ⋅ (1)n – 1 for n ≥ 1

C)

an = (1) ⋅ (1)n – 1 for n ≥ 2

D)

an = (–1) ⋅ (–1)n – 1 for n < 1