[tex]\displaystyle a=(3 \sqrt{2} -2 \sqrt{3} )(3 \sqrt{2} +2 \sqrt{3} )-(2- \sqrt{3} )^2- \sqrt{48} \\ a=18-12-(2^2-2 \cdot 2 \cdot \sqrt{3} + \sqrt{3} ^2)-4 \sqrt{3} \\ a=6-(4-4 \sqrt{3} +3)-4 \sqrt{3} \\ a=6-(7-4 \sqrt{3} )-4 \sqrt{3} \\ a=6-7+4 \sqrt{3} -4 \sqrt{3} \\ a=-1[/tex]