If a1= 7 and r=3, find a4

a4 = 189

Step-by-step explanation:

Geometric sequence:

In a geometric sequence, the quotient r between consecutive terms is always the same.

The nth term of the sequence is given by:

In which is the first term.

In this question:

The fourth term is:

So

a4 = 189

correct answer:

i^31 = -i