Rule 1
a (b + c) = ab + ac
Rule 2
(a+b) (c+d) = ac + ad + bc + bd
Rule 3
(a+b) (a+b) = a² + 2ab + b²
Rule 4
(a-b) (a-b) = a² - 2ab + b²
Rule 5
(a+b) (a-b) = a² - b²