Ответ:

[tex]\displaystyle (3-x-y)(3+x+y)[/tex]

Объяснение:

[tex]\displaystyle 9-x^2-2xy-y^2=9-(x^2+2xy+y^2)=9-(x+y)^2=(3-(x+y))(3+(x+y))=(3-x-y)(3+x+y)[/tex]