a.
[tex] \sqrt{2 } + \sqrt{28} \div \sqrt{24} = \sqrt{2} + \sqrt{28 \div 4} = \sqrt{2} + \sqrt{2} = 2 \sqrt{2} [/tex]
[tex] \sqrt{3} \sqrt{6} - \sqrt{32} = \sqrt{3 \times 6} - \sqrt{32} = \sqrt{18} - 4 \sqrt{2} = 3 \sqrt{2} - 4 \sqrt{2} = - \sqrt{2} [/tex]
[tex] \sqrt{6} \div \sqrt{2} - \sqrt{60} \div \sqrt{5} = \sqrt{3} - \sqrt{12} = \sqrt{3} - 2 \sqrt{3} = - \sqrt{3} [/tex]
[tex] \sqrt{2}(2 \sqrt{3}) - \sqrt{42} \div \sqrt{7} = 2 \sqrt{6} - \sqrt{6} \times \sqrt{7} \div \sqrt{7} =2 \sqrt{6} - \sqrt{6} = \sqrt{6} [/tex]
