Above you have the general form of special product call difference of squares. In this case you get as result a binomial (a math expression with two terms x² and a²) that is product of sum (+) and difference (-) of two terms (x and a)
Then, the given expression is:
[tex](x+6)(x-6)=x^2-6^2=x^2-36[/tex]d. Binomial that is product of sum and difference of two terms (the two terms are x and 6)