Question

Find an explicit formula for the geometric sequence −1,−7,−49,−343,...-1\,,-7\,,-49\,,-343,... −1,−7,−49,−343

Answer 1

So we see it times 7 each time
starting with -1

geometric
an=a1(r)^(n-1)
a1=first term
r=common ratio
first term is -1
r=7

$a_n=-1(7)^{n-1}$ is the formula
also can look like this:
$f(n)=-1(7)^{n-1}$