If the first 4 terms of a geometric sequence are {7, 21, 63, 189), then the formula for the nth term in the sequence is?

Answer: 7 * (3^n - 1)

Step-by-step explanation:

This is a geometric progression which has its nth term to be

Tn = ar^n - 1. Now from the question given, the sequence are 7, 21, 63, 189. This is an example of a finite sequence, To find the common ratio, you divide the second term by the first term. So

r = 21/7

= 3., a = 7

Now to find the nth term put the values in the formula above.

Tn = ar^n-1

= 7 (3) ^n - 1)

= 7 * (3^n - 1).

Note, it is not 21^n - 1.