[tex](3-\sqrt{2}x)^{2}+(\sqrt{6}+\sqrt{3}x)^{2}-(\sqrt{15}-\sqrt{2}x)(\sqrt{15}+\sqrt{2}x)[/tex]
[tex]9-6\sqrt{2}x+2x^{2}+(6+2\sqrt{18}x+3x^{2})-(15-2x^{2})[/tex]
[tex]9-6\sqrt{2}x+2x^{2}+6+2\cdot 3\sqrt{2}x+3x^{2}-15+2x^{2}[/tex]
[tex]9-6\sqrt{2}+2x^{2}+6+6\sqrt{2}x+3x^{2}-15+2x^{2}[/tex]
[tex]7x^{2}-6+6=7x^{2}[/tex]
