Write an explicit formula for the sequence: 1/2, - 1/4, 1/8, - 1/6.

i know that the ratio is - 0.5 but im confused on how to write this into a explicit formula.

This is a geometric sequence because there is a common ration. Which means that each term is a constant multiple of the previous term ... in this case:

r = (-1/4) / (1/2) = (1/8) / (-1/4) = - 1/2

Any geometric sequence can be expressed as:

a (n) = ar^ (n-1), a=initial term, r=common ratio, n=term number ... in this case:

a (n) = (1/2) (-1/2) ^ (n-1)