X ^2 y^2 - 81 ;=(xy)^2-9^2=(xy-9)(xy+9)
(5a^2-a+3)^2-(5a^2)^2=(5a^2-a+3-5a^2)(5a^2-a+3+5a^2)=(3-a)(10a^2-a+3)
X ^2 y^2 - 81 ;=(xy)^2-9^2=(xy-9)(xy+9)
(5a^2-a+3)^2-(5a^2)^2=(5a^2-a+3-5a^2)(5a^2-a+3+5a^2)=(3-a)(10a^2-a+3)