Given the following pair of conjugates:
[tex]\mleft(xy-9\mright)\mleft(xy+9\mright)[/tex]As shown, the same terms and the different signs
This is called the factor of the square difference
The product will be as follows:
[tex]\mleft(xy-9\mright)\mleft(xy+9\mright)=(xy)^2-(9)^2=x^2y^2-81[/tex]So, the answer will be:
[tex]x^2y^2-81[/tex]