Identify the Sequence -64 , -32 , -16 , -8

This is a geometric sequence since there is a common ratio between each term. In this case, multiplying the previous term in the sequence by ${\displaystyle \frac{1}{2}}$ gives the next term. In other words, ${\displaystyle a_n=a_1{r}^{n-1}}$.

This is the form of a geometric sequence.

Substitute in the values of ${\displaystyle a_1=-64}$ and ${\displaystyle r=\frac{1}{2}}$.

Apply the product rule to ${\displaystyle \frac{1}{2}}$.

One to any power is one.

Combine ${\displaystyle -64}$ and ${\displaystyle \frac{1}{2^{n-1}}}$.