Answer
a. $a_{n} = -3(-2)^{n-1}$
b. Fourth term: 24
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 = -3 and r=-2. Plug these values into the formula to get a formula for the nth term of this sequence.
b. To find the fourth term plug in n = 4 into the sequence: $a_{n} = -3(-2)^{4-1} = -3(-2)^{3} = 24$
