Tính
a) \(\left( {\sqrt {\frac{4}{3}} + \sqrt 3 } \right)\sqrt 6 \)
b) \(\sqrt {18} :\sqrt 6 + \sqrt 8 .\sqrt {\frac{{27}}{2}} \)
c) \({\left( {1 - 2\sqrt 5 } \right)^2}\)
Dựa vào VD5 trang 55 làm tương tự.
a) \(\left( {\sqrt {\frac{4}{3}} + \sqrt 3 } \right)\sqrt 6 = \sqrt {\frac{4}{3}} .\sqrt 6 + \sqrt 3 .\sqrt 6 \) \(= \sqrt {\frac{{24}}{3}} + \sqrt {18} \)\(=\sqrt 8 + \sqrt {18} \)\(= \sqrt {2.4} + \sqrt {2.9} \)\(= 2\sqrt 2 + 3\sqrt 2 \)\(= 5\sqrt 2 \)
b) \(\sqrt {18} :\sqrt 6 + \sqrt 8 .\sqrt {\frac{{27}}{2}} \)\( = \sqrt {\frac{{18}}{6}} + \sqrt {8.\frac{{27}}{2}} \)\( = \sqrt 3 + \sqrt {108} \)\( = \sqrt 3 + \sqrt {36.3} \)\( = \sqrt 3 + 6\sqrt 3 \)\( = 7\sqrt 3 \)
c) \({\left( {1 - 2\sqrt 5 } \right)^2} = 1 - 4\sqrt 5 + 20 = 21 - 4\sqrt 5 \)