The nth term of a geometric sequence is
an = a1 • r n-1 , where a1 is the first term and r is the common ratio.
i need

1) a = 1 , r = 3

2) a = 8, r =

3) a = 4, r = -4

Step-by-step explanation:

Since we have given that

1) 1, 3, 9,27, ..........

Here, first term = a = 1

r = Common ratio is given by

2) 8, 4, 2, 1, ..........

Here, first term = a = 8

r = common ratio is given by

3) 4,-16,64,-256,.............

Here, first term = a = 4

r =  common ratio is given by

Hence, 1) a = 1 , r = 3

2) a = 8, r =

3) a = 4, r = -4

Series                           First term(a_1)             common ratio(r)        

1,3,9,27,...                             1                                   3

8,4,2,1,....                              8                                 1/2

4,-16,64,-256,...                    4                                  -4          

We know that the nth term of a geometric series is given by:

where is the first term and r is the common ratio.

1)

The first sequence is:

1,3,9,27,....

The first term i.e.

and if r is the common ratio then,

Since, from the sequence we have:

This means that:

2)

Second sequence is:

8,4,2,1,....

The first term i.e.

and if r is the common ratio then,

Since, from the sequence we have:

This means that:

3)

Third sequence is:

4,-16,64,-256,...  

The first term i.e.

and if r is the common ratio then,

Since, from the sequence we have:

This means that:

answer: you need the equation in the question so i can answer it

step-by-step explanation: