Khử mẫu trong dấu căn: a) \(2a.\sqrt {\frac{3}{5}} ;\) b) \( - 3x.\sqrt {\frac{5}{x}} \) (x > 0); c) \[ - \sqrt {\frac{{3a}}{b}} \] (a ≥ 0, b > 0).

a) \(2a.\sqrt {\frac{3}{5}} = 2a.\sqrt {\frac{{3.5}}{{{5^2}}}} = 2a.\frac{{\sqrt {15} }}{{\sqrt {25} }} = \frac{{2a\sqrt {15} }}{5}.\)

b) \[ - 3x.\sqrt {\frac{5}{x}} = - 3x.\sqrt {\frac{{5.x}}{{{x^2}}}} = - 3x.\frac{{\sqrt {5x} }}{x} = - 3\sqrt {5x} .\]

c) \( - \sqrt {\frac{{3a}}{b}} = - \sqrt {\frac{{3ab}}{{{b^2}}}} = \frac{{ - \sqrt {3ab} }}{b}.\)