"at a locus with a dominant and a recessive allele in hardy-weinberg equilibrium, 9% of the individuals are homozygous for the recessive allele. what is the frequency of the dominant allele in the population? "

Dominant allele = p
Recessive allele = q, p+q=1, since those are the only alleles which contribute to this trait
For genotype frequencies, we square both side of that equation: (p+q)2 = 1^2 --> p2 + 2pq + q2 = 1, where
p2 = homozygous dominant frequency
q2 = homozygous recessive frequency
2pq = heterozygous frequency
q2 = .09 --> q = 0.3, which is the same as 30% --> p+q=1, so p = 1-0.3 = 0.6
Or 60% of this trait within this population contains the dominant (p) allele