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Tính :
a) \(\dfrac{{\sqrt {27} }}{{\sqrt 3 }}\); b) \(\dfrac{{\sqrt {0,4} }}{{\sqrt {0,9} }}\);
c) \(\dfrac{{\sqrt {320} }}{{\sqrt {20} }}\); d) \(\dfrac{{\sqrt {{3^5}{{.2}^3}} }}{{\sqrt {{6^7}} }}\).
Sử dụng công thức: \(\dfrac{{\sqrt A }}{{\sqrt B }} = \sqrt {\dfrac{A}{B}} .\)
\(\begin{array}{l}a)\;\dfrac{{\sqrt {27} }}{{\sqrt 3 }} = \sqrt {\dfrac{{27}}{3}} = \sqrt 9 = 3 & & & b)\;\dfrac{{\sqrt {0,4} }}{{\sqrt {0,9} }} = \sqrt {\dfrac{{0,4}}{{0,9}}} = \sqrt {\dfrac{4}{9}} = \dfrac{{\sqrt 4 }}{{\sqrt 9 }} = \dfrac{2}{3}\\c)\;\dfrac{{\sqrt {320} }}{{\sqrt {20} }} = \sqrt {\dfrac{{320}}{{20}}} = \sqrt {16} = 4 & & & d)\;\dfrac{{\sqrt {{3^5}{{.2}^3}} }}{{\sqrt {{6^7}} }} = \sqrt {\dfrac{{{3^5}{{.2}^3}}}{{{3^7}{{.2}^7}}}} = \sqrt {\dfrac{1}{{{3^2}{{.2}^4}}}} = \dfrac{1}{{\sqrt {{3^2}} .\sqrt {{2^4}} }} = \dfrac{1}{{{{3.2}^2}}} = \dfrac{1}{{12}}.\end{array}\)