Tính: a) \(\sqrt {99} :\sqrt {11} ;\) b) \(\sqrt {7,84} ;\) c) \(\sqrt {1815} :\sqrt {15} .\)

a) \(\sqrt {99} :\sqrt {11} = \sqrt {99:11} = \sqrt 9 = 3.\)

b) \[\sqrt {7,84} = \sqrt {\frac{{784}}{{100}}} = \sqrt {\frac{{4.196}}{{4.25}}} = \sqrt {\frac{{196}}{{25}}} = \sqrt {{{\left( {\frac{{14}}{5}} \right)}^2}} = \frac{{14}}{5}.\]

c) \[\sqrt {1815} :\sqrt {15} = \sqrt {1815:15} = \sqrt {121} = 11.\]