Answer
a. $a_{n} = 7(4)^{n-1}$
b. 4th term: 448
Work Step by Step
a. $a_{n} = a(r)^{n-1}$ is the formula for the nth term of a geometric sequence. In this case a = 7 and r=4. Plug these values into the formula to get a formula for the nth term of the sequence.
b. To find the fourth term plug in n = 4 into the sequence: $a_{n} = 7(4)^{4-1} = 7(4)^{3} = 448$
