Question

b(n) = 1 \left(-2\right)^{n - 1

Where is the fourth sequence?

Answer 1

I assume you mean the 4th term of the sequence given by b(n) = 1·(-2)^{n-1}.

Compute b(4): b(4) = 1·(-2)^{4-1} = (-2)^3 = -8.

First few terms: b(1)=1, b(2)=-2, b(3)=4, b(4)=-8, b(5)=16, ...

If you meant something else by “Where is the fourth sequence?” please clarify.