Answer :
[tex]x^{4}-x^{2}y^{2}-2y^{4}[/tex]
[tex]=x^{4}-2x^{2}y^{2}+x^{2}y^{2}-2y^{4}[/tex]
[tex]=x^{2}(x^{2}-2y^{2})+y^{2}(x^{2}-2y^{2})[/tex]
[tex]=(x^{2}-2y^{2})(x^{2}+y^{2})[/tex]
[tex]=x^{4}-2x^{2}y^{2}+x^{2}y^{2}-2y^{4}[/tex]
[tex]=x^{2}(x^{2}-2y^{2})+y^{2}(x^{2}-2y^{2})[/tex]
[tex]=(x^{2}-2y^{2})(x^{2}+y^{2})[/tex]