Đáp án: B=2 Giải thích các bước giải: \(\begin{array}{l}B = \sqrt {2 – \sqrt 3 } .\sqrt 2 \left( {\sqrt 3 – 1} \right)\left( {2 + \sqrt 3 } \right)\\ = \sqrt {4 – 2\sqrt 3 } .\left( {\sqrt 3 – 1} \right)\left( {2 + \sqrt 3 } \right)\\ = \sqrt {3 – 2\sqrt 3 .1 + 1} .\left( {\sqrt 3 – 1} \right)\left( {2 + \sqrt 3 } \right)\\ = \sqrt {{{\left( {\sqrt 3 – 1} \right)}^2}} .\left( {\sqrt 3 – 1} \right)\left( {2 + \sqrt 3 } \right)\\ = \left( {\sqrt 3 – 1} \right)\left( {\sqrt 3 – 1} \right)\left( {2 + \sqrt 3 } \right)\\ = \left( {3 – 2\sqrt 3 + 1} \right)\left( {2 + \sqrt 3 } \right)\\ = \left( {4 – 2\sqrt 3 } \right)\left( {2 + \sqrt 3 } \right)\\ = 2\left( {2 – \sqrt 3 } \right)\left( {2 + \sqrt 3 } \right)\\ = 2\left( {4 – 3} \right) = 2\\C = \sqrt {7 – 3\sqrt 5 } \left( {7 + 3\sqrt 5 } \right).\sqrt 2 \left( {3 + \sqrt 5 } \right)\\ = \sqrt {14 – 6\sqrt 5 } .\left( {7 + 3\sqrt 5 } \right)\left( {3 + \sqrt 5 } \right)\\ = \sqrt {9 – 2.3.\sqrt 5 + 5} .\left( {7 + 3\sqrt 5 } \right)\left( {3 + \sqrt 5 } \right)\\ = \sqrt {{{\left( {3 – \sqrt 5 } \right)}^2}} \left( {7 + 3\sqrt 5 } \right)\left( {3 + \sqrt 5 } \right)\\ = \left( {3 – \sqrt 5 } \right)\left( {3 + \sqrt 5 } \right)\left( {7 + 3\sqrt 5 } \right)\\ = \left( {9 – 5} \right)\left( {7 + 3\sqrt 5 } \right)\\ = 4\left( {7 + 3\sqrt 5 } \right)\\ = 28 + 12\sqrt 5 \\D = \sqrt 2 \left( {3 – \sqrt 5 } \right).\left( {6 – \sqrt {35} } \right).\sqrt {6 + \sqrt {35} } \\ = \left( {3 – \sqrt 5 } \right).\left( {6 – \sqrt {35} } \right)\sqrt {12 + 2\sqrt {35} } \\ = \left( {3 – \sqrt 5 } \right).\left( {6 – \sqrt {35} } \right)\sqrt {7 + 2.\sqrt 7 .\sqrt 5 + 5} \\ = \left( {3 – \sqrt 5 } \right).\left( {6 – \sqrt {35} } \right)\sqrt {{{\left( {\sqrt 7 + \sqrt 5 } \right)}^2}} \\ = \left( {3 – \sqrt 5 } \right).\left( {6 – \sqrt {35} } \right)\left( {\sqrt 7 + \sqrt 5 } \right)\\ = \left( {3 – \sqrt 5 } \right)\left( {6\sqrt 7 + 6\sqrt 5 – 7\sqrt 5 – 5\sqrt 7 } \right)\\ = \left( {3 – \sqrt 5 } \right)\left( {\sqrt 7 – \sqrt 5 } \right)\\ = 3\sqrt 7 – 3\sqrt 5 – \sqrt {35} + 5\end{array}\) Reply
Đáp án:
B=2
Giải thích các bước giải:
\(\begin{array}{l}
B = \sqrt {2 – \sqrt 3 } .\sqrt 2 \left( {\sqrt 3 – 1} \right)\left( {2 + \sqrt 3 } \right)\\
= \sqrt {4 – 2\sqrt 3 } .\left( {\sqrt 3 – 1} \right)\left( {2 + \sqrt 3 } \right)\\
= \sqrt {3 – 2\sqrt 3 .1 + 1} .\left( {\sqrt 3 – 1} \right)\left( {2 + \sqrt 3 } \right)\\
= \sqrt {{{\left( {\sqrt 3 – 1} \right)}^2}} .\left( {\sqrt 3 – 1} \right)\left( {2 + \sqrt 3 } \right)\\
= \left( {\sqrt 3 – 1} \right)\left( {\sqrt 3 – 1} \right)\left( {2 + \sqrt 3 } \right)\\
= \left( {3 – 2\sqrt 3 + 1} \right)\left( {2 + \sqrt 3 } \right)\\
= \left( {4 – 2\sqrt 3 } \right)\left( {2 + \sqrt 3 } \right)\\
= 2\left( {2 – \sqrt 3 } \right)\left( {2 + \sqrt 3 } \right)\\
= 2\left( {4 – 3} \right) = 2\\
C = \sqrt {7 – 3\sqrt 5 } \left( {7 + 3\sqrt 5 } \right).\sqrt 2 \left( {3 + \sqrt 5 } \right)\\
= \sqrt {14 – 6\sqrt 5 } .\left( {7 + 3\sqrt 5 } \right)\left( {3 + \sqrt 5 } \right)\\
= \sqrt {9 – 2.3.\sqrt 5 + 5} .\left( {7 + 3\sqrt 5 } \right)\left( {3 + \sqrt 5 } \right)\\
= \sqrt {{{\left( {3 – \sqrt 5 } \right)}^2}} \left( {7 + 3\sqrt 5 } \right)\left( {3 + \sqrt 5 } \right)\\
= \left( {3 – \sqrt 5 } \right)\left( {3 + \sqrt 5 } \right)\left( {7 + 3\sqrt 5 } \right)\\
= \left( {9 – 5} \right)\left( {7 + 3\sqrt 5 } \right)\\
= 4\left( {7 + 3\sqrt 5 } \right)\\
= 28 + 12\sqrt 5 \\
D = \sqrt 2 \left( {3 – \sqrt 5 } \right).\left( {6 – \sqrt {35} } \right).\sqrt {6 + \sqrt {35} } \\
= \left( {3 – \sqrt 5 } \right).\left( {6 – \sqrt {35} } \right)\sqrt {12 + 2\sqrt {35} } \\
= \left( {3 – \sqrt 5 } \right).\left( {6 – \sqrt {35} } \right)\sqrt {7 + 2.\sqrt 7 .\sqrt 5 + 5} \\
= \left( {3 – \sqrt 5 } \right).\left( {6 – \sqrt {35} } \right)\sqrt {{{\left( {\sqrt 7 + \sqrt 5 } \right)}^2}} \\
= \left( {3 – \sqrt 5 } \right).\left( {6 – \sqrt {35} } \right)\left( {\sqrt 7 + \sqrt 5 } \right)\\
= \left( {3 – \sqrt 5 } \right)\left( {6\sqrt 7 + 6\sqrt 5 – 7\sqrt 5 – 5\sqrt 7 } \right)\\
= \left( {3 – \sqrt 5 } \right)\left( {\sqrt 7 – \sqrt 5 } \right)\\
= 3\sqrt 7 – 3\sqrt 5 – \sqrt {35} + 5
\end{array}\)