k, so we see it is not increasing by same value, so it isn't arithmetic sequence
geometric, times 4 each time
f(n)=a1(r)^(n-1)
r=common ratio
a1=first term
so
first term is -2 and common ratio is 4
[tex]f(n)=-2(4)^{n-1}[/tex]
or simply
[tex]f(n)= (\frac{-1}{2} )(4^n)[/tex]
