Answer:
A. an = 1(4)^n-1
Step-by-step explanation:
Geometric sequence:
In a geometric sequence, the quotient between consecutive terms is always the same, called common ratio, and the sequence is given by:
[tex]a_n = a_1(q)^{n-1}[/tex]
In which [tex]a_1[/tex] is the first term and q is the common ratio.
We are given the following sequence:
[tex]a_1 = 1[/tex]
[tex]a_n = 4a_{n-1}[/tex]
So
[tex]a_2 = 4a_1 = 4[/tex]
[tex]a_3 = 4a_2 = 16[/tex]
[tex]a_4 = 4a_3 = 64[/tex]
That is, the quotient between consecutive terms is 4, so [tex]q = 4[/tex].
The first term is already given, [tex]a_1 = 1[/tex]. So
[tex]a_n = a_1(q)^{n-1}[/tex]
[tex]a_n = 1(4)^{n-1}[/tex]
And thus, the correct answer is given by option A.
