Before proceeding to part c.) we need to confess that the statement doesn't actually make sense! The problem is that although we assume that M6=0 it is entirely possible that some of the b's a zero , and thus the sequence .f a=b g may not make sense.To understand that this is really not a problem we have the following lemma which tells us that we can be sure that,at least even tually,the b's are non zero,and thus,since the bebingning of a sequence does not a ectits limit,we can ignore those first terms where some of the b's may be zero.