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\(Q=\left(3-\sqrt{5}\right)\sqrt{3+\sqrt{5}}+\left(3+\sqrt{5}\right)\sqrt{3-\sqrt{5}}\)
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Q
22 tháng 6 2017
1) \(P=\left(4+\sqrt{15}\right)\left(\sqrt{10}-\sqrt{6}\right)\sqrt{4-\sqrt{15}}\)
\(=\left(4\sqrt{10}-4\sqrt{6}+\sqrt{150}-\sqrt{90}\right)\sqrt{4-\sqrt{15}}\)
\(=\left(4\sqrt{10}-4\sqrt{6}+5\sqrt{6}-3\sqrt{10}\right)\sqrt{4-\sqrt{15}}\)
\(=\left(\sqrt{10}+\sqrt{6}\right)\sqrt{4-\sqrt{15}}\)
\(=\sqrt{\left(\sqrt{10}+\sqrt{6}\right)^2}\sqrt{4-\sqrt{15}}\)
\(=\sqrt{\left(\sqrt{10}+\sqrt{6}\right)^2+\left(4-\sqrt{15}\right)}\)
\(=\sqrt{\left(10+2\sqrt{60}+6\right)\cdot\left(4-\sqrt{15}\right)}\)
\(=\sqrt{\left(10+4\sqrt{15}+6\right)\cdot\left(4-\sqrt{15}\right)}\)
\(=\sqrt{\left(16+4\sqrt{15}\right)\cdot\left(4-\sqrt{15}\right)}\)
\(=\sqrt{4\left(4+\sqrt{15}\right)\cdot\left(4-\sqrt{15}\right)}\)
\(=\sqrt{4\left(16-15\right)}\)
\(=\sqrt{4\cdot1}\)
\(=\sqrt{4}\)
\(=2\)
2) \(Q=\left(3-\sqrt{5}\right)\sqrt{3+\sqrt{5}}+\left(3+\sqrt{5}\right)\sqrt{3-\sqrt{5}}\)
\(=\sqrt{\left(3-\sqrt{5}\right)^2}\sqrt{3+\sqrt{5}}+\sqrt{\left(3+\sqrt{5}\right)^2}\sqrt{3-\sqrt{5}}\)
\(=\sqrt{\left(3-\sqrt{5}\right)^2\cdot\left(3+\sqrt{5}\right)}+\sqrt{\left(3+\sqrt{5}\right)^2\cdot\left(3-\sqrt{5}\right)}\)
\(=\sqrt{\left(9-6\sqrt{5}+5\right)\cdot\left(3+\sqrt{5}\right)}+\sqrt{\left(9+6\sqrt{5}+5\right)\cdot\left(3-\sqrt{5}\right)}\)
\(=\sqrt{\left(14-6\sqrt{5}\right)\cdot\left(3+\sqrt{5}\right)}+\sqrt{\left(9+6\sqrt{5}+5\right)\cdot\left(3-\sqrt{5}\right)}\)
\(=\sqrt{42+14\sqrt{5}-18\sqrt{5}-30}+\sqrt{42-14\sqrt{5}+18\sqrt{5}-30}\)
\(=\sqrt{12-4\sqrt{5}}+\sqrt{12+4\sqrt{5}}\)
24 tháng 7 2017
\(\sqrt{3-\sqrt{5}}\sqrt{3-\sqrt{5}}\)\(\sqrt{3+\sqrt{5}}\)\(+\sqrt{3+\sqrt{5}}\sqrt{3+\sqrt{5}}\sqrt{3-\sqrt{5}}\)
=\(\sqrt{3-\sqrt{5}}\cdot\sqrt{3^2-5}+\sqrt{3+\sqrt{5}}\cdot\sqrt{3^2-5}\)=\(2\left(\sqrt{3-\sqrt{5}}+\sqrt{3+\sqrt{5}}\right)=\sqrt{2}\left(\sqrt{2\cdot3-2\sqrt{5}}+\sqrt{2\cdot3+2\sqrt{5}}\right)\) =\(=\sqrt{2}\left(\sqrt{5}-1+\sqrt{5}+1\right)=2\sqrt{10}\)
b tuong tu nha ban ^.^
21 tháng 8 2017
(14,78-a)/(2,87+a)=4/1
14,78+2,87=17,65
Tổng số phần bằng nhau là 4+1=5
Mỗi phần có giá trị bằng 17,65/5=3,53
=>2,87+a=3,53
=>a=0,66.
6 tháng 9 2019
\( \left( {\sqrt 2 + \sqrt 3 + \sqrt 5 } \right)\left( {\sqrt 2 + \sqrt 3 - \sqrt 5 } \right)\left( {\sqrt 2 - \sqrt 3 + \sqrt 5 } \right)\left( { - \sqrt 2 + \sqrt 3 + \sqrt 5 } \right)\\ = \left[ {{{\left( {\sqrt 2 + \sqrt 3 } \right)}^2} - 5} \right]\left( {\sqrt 5 + \sqrt 2 - \sqrt 3 } \right)\left( {\sqrt 5 - \sqrt 2 + \sqrt 3 } \right)\\ = \left( {2 + 2\sqrt 6 + 3 - 5} \right)\left[ {5 - {{\left( {\sqrt 2 - \sqrt 3 } \right)}^2}} \right]\\ = 2\sqrt 6 \left[ {5 - \left( {2 - 2\sqrt 6 + 3} \right)} \right]\\ = 2\sqrt 6 .2\sqrt 6 \\ = 4\sqrt {36} = 4.6 = 24 \)
\(Q=\dfrac{\left(3-\sqrt{5}\right)\cdot\sqrt{6+2\sqrt{5}}+\left(3+\sqrt{5}\right)\sqrt{6-2\sqrt{5}}}{\sqrt{2}}\)
\(=\dfrac{\left(3-\sqrt{5}\right)\left(\sqrt{5}+1\right)+\left(3+\sqrt{5}\right)\left(\sqrt{5}-1\right)}{\sqrt{2}}\)
\(=\dfrac{3\sqrt{5}+3-5-\sqrt{5}+3\sqrt{5}-3+5-\sqrt{5}}{\sqrt{2}}\)
\(=\dfrac{4\sqrt{5}}{\sqrt{2}}=2\sqrt{10}\)
giúp mình với ạ