Biểu thức $\sqrt {x - 3}$  có nghĩa khi

$\sqrt {{A^2}B}  = A\sqrt B$

$\sqrt {{A^2}B}  =  - A\sqrt B$

$\sqrt {{A^2}B}  = -B\sqrt A$

$\sqrt {{A^2}B}  = B\sqrt A$

$\dfrac{9}{{13}}$

$\dfrac{9}{{169}}$

$\dfrac{3}{{13}}$

$\dfrac{{13}}{9}$

$14a$

$20a$

$9a$

$- 8a$

$\sqrt {ab}  = a\sqrt b$

$\sqrt a \sqrt b  = b\sqrt a$

$\sqrt a .\sqrt b  = \sqrt {ab}$

$\sqrt {ab}  = \dfrac{{\sqrt a }}{{\sqrt b }}$

$5\sqrt 3  > 4\sqrt 5$

$5\sqrt 3  = 4\sqrt 5$

$5\sqrt 3  \ge 4\sqrt 5$

$5\sqrt 3  < 4\sqrt 5$

$\sqrt[3]{{ab}} = \sqrt a .\sqrt b$

$\dfrac{{\sqrt[3]{a}}}{{\sqrt[3]{b}}} = \dfrac{a}{b}$ với $b \ne 0$

${\left( {\sqrt[3]{a}} \right)^3} =  - a\, khi\,a < 0$

$\dfrac{{\sqrt[3]{a}}}{{\sqrt[3]{b}}} = \sqrt[3]{{\dfrac{a}{b}}}$ với $b \ne 0$