a)
[tex]2 \sqrt{3} - \sqrt{12} = 2 \sqrt{3} - \sqrt{4 \times 3} = 2 \sqrt{3} - 2 \sqrt{3} = 0[/tex]
b)
[tex] \sqrt{15} - 2 \sqrt{5} = \sqrt{15} - \sqrt{4 \times 5} = \sqrt{15} - \sqrt{20} = \boxed{ ( - )}[/tex]
c)
[tex]3 \sqrt{2} - \sqrt{19} = \sqrt{9 \times 2} - \sqrt{19} = \sqrt{18} - \sqrt{19} = \boxed{ ( - )}[/tex]
d)
[tex]3 \sqrt{3} - \sqrt{20} = \sqrt{9 \times 3} - \sqrt{20} = \sqrt{27} - \sqrt{20} = \boxed{( + )}[/tex]
ODP.B
