Question

What is the closed form definition for 4, -12, 36, -108?

Answer 1

we see that

`\begin{gathered} (-12)/(4)=-3 \\ (36)/(-12)=-3 \\ (-108)/(36)=-3 \end{gathered}`

Then, we have a geometric sequence, and each time we need to muliply by -3 starting from 4, so the closed-form is

`t(n)=4(-3)^(n-1)`

so, the answer is the second one.