Find an equation for the nth term of the sequence.
-2, -8, -32, -128,

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

or simply