[tex]( \sqrt{6} ) {}^{2} = 6 \\ ( - \sqrt{21} ) {}^{2} = 21 \\ (3 \sqrt{2} ) {}^{2} = 9 \times 2 = 18 \\ ( - 4 \sqrt{5} ) {}^{2} = 16 \times 5 = 80[/tex]