How does the Hardy - Weinberg's expression ( p^2 +2pq + q^2 = 1) explain that genetic equilibrium is maintained in a population?

The gene pool i.e., the total genes and their alleles in a population tend to remain constant, This is called genetic equilibrium. Sum total of all allelic frequencies is 1 Individual frequencies, can be named p,q, etc. In a diploid, p and q represent the frequency of allele A and allele n. The frequency of AA individuals in a population is simply p². This is simply stated in another ways, i.e., the probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual is simply the product of the probabilities, i.e., p². Similarly of aa is q², of Aa 2pq. Hence, p² +2pq + q² = 1. When frequency measured, differs from expected values, the difference (direction) indicates the extent of evolutionary change. Disturbance in genetic equilibrium, or Hardy- Weinberg equilibrium, i.e., change of frequency of alleles in a population would then be interpreted as resulting in evolution.