The first term in the sequence is -2 and the fifth term is -1/8 what is the common ratio
since you used the term 'common ratio' I must assume your sequence is geometric
term(5) = ar^4
ar^4 = -2(r^4) = -1/8
r^4 = 1/16
take 4th root
r = ± 1/2
term(5) = ar^4
ar^4 = -2(r^4) = -1/8
r^4 = 1/16
take 4th root
r = ± 1/2