Question

Use the Distributive Property to find (z−5)(z+3).

Answer 1

Consider, $(z-5)(z+3)$. Let's say $a = z-5$ then the problem reduces to $a(z+3)=za+3a$. (Do you understand this step?)

So then replacing a again with our definition we get, $z(z-5)+3(z-5)=z^2-5z+3z-15=z^2-2z-15$.