Question

Khử mẫu trong dấu căn:

a) \(2a.\sqrt{\dfrac{3}{5}}\);                  b) \(-3x.\sqrt{\dfrac{5}{x}}\) (với x > 0);                c) \(\sqrt{-\dfrac{3a}{b}}\) (a ≥ 0, b > 0).

Answer 1

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

b) \( - 3x.\sqrt {\frac{5}{x}}  =  - 3x.\frac{{\sqrt 5 .\sqrt x }}{{\sqrt x .\sqrt x }} =  - 3x.\frac{{\sqrt {5x} }}{x} =  - 3\sqrt {5x} \)

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