giá tr của biểu thưc :\(\sqrt{15-6\sqrt{6}}+\sqrt{15+6\sqrt{6}}\)
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3
21 tháng 8 2021
\(B=\left(4+\sqrt{15}\right)\left(\sqrt{10}-\sqrt{6}\right)\sqrt{4-\sqrt{15}}\\ B=\left(4+\sqrt{15}\right)\left(\sqrt{5}-\sqrt{3}\right)^2\\ B=\left(4+\sqrt{15}\right)\left(8-2\sqrt{15}\right)\\ B=2\)
21 tháng 8 2021
\(\left(4+\sqrt{15}\right)\left(\sqrt{10}-\sqrt{6}\right)\sqrt{4-\sqrt{15}}=\sqrt{4+\sqrt{15}}.\sqrt{2}\left(\sqrt{5}-\sqrt{3}\right).\sqrt{\left(4+\sqrt{15}\right)\left(4-\sqrt{15}\right)}=\sqrt{8+2\sqrt{15}}\left(\sqrt{5}-\sqrt{3}\right).\sqrt{16-15}=\sqrt{\left(\sqrt{3}\right)^2+2\sqrt{3}.\sqrt{5}+\left(\sqrt{5}\right)^2}\left(\sqrt{5}-\sqrt{3}\right)\)\(=\sqrt{\left(\sqrt{5}+\sqrt{3}\right)^2}.\left(\sqrt{5}-\sqrt{3}\right)=\left|\sqrt{5}+\sqrt{3}\right|\left(\sqrt{5}-\sqrt{3}\right)=\left(\sqrt{5}+\sqrt{3}\right)\left(\sqrt{5}-\sqrt{3}\right)=5-3=2\)
NN
1
16 tháng 9 2021
\(=\sqrt{4+\sqrt{15}}\left(\sqrt{4+\sqrt{15}}\cdot\sqrt{4-\sqrt{15}}\right)\left(\sqrt{10}-\sqrt{6}\right)\\ =\sqrt{4+\sqrt{15}}\left(16-15\right)\left(\sqrt{10}-\sqrt{6}\right)\\ =\sqrt{2\left(4+\sqrt{15}\right)}\left(\sqrt{5}-\sqrt{3}\right)\\ =\sqrt{8+2\sqrt{15}}\left(\sqrt{5}-\sqrt{3}\right)\\ =\left(\sqrt{5}+\sqrt{3}\right)\left(\sqrt{5}-\sqrt{3}\right)=5-3=2\)
HT
1
9 tháng 10 2021
\(\sqrt{15-6\sqrt{6}}+\sqrt{33-12\sqrt{6}}\)
\(=\sqrt{\left(3-\sqrt{6}\right)^2}+\sqrt{\left(2\sqrt{6}-3\right)^2}\)
\(=3-\sqrt{6}+2\sqrt{6}-3=\sqrt{6}\)
H9
HT.Phong (9A5)
CTVHS
5 tháng 9 2023
a) \(\left(\sqrt{14}+\sqrt{6}\right)\sqrt{5-\sqrt{21}}\)
\(=\sqrt{14}\cdot\sqrt{5-\sqrt{21}}+\sqrt{6}\cdot\sqrt{5-\sqrt{21}}\)
\(=\sqrt{14\cdot\left(5-\sqrt{21}\right)}+\sqrt{6\cdot\left(5-\sqrt{21}\right)}\)
\(=\sqrt{70-14\sqrt{21}}+\sqrt{30-6\sqrt{21}}\)
\(=\sqrt{7^2-2\cdot7\cdot\sqrt{21}+\left(\sqrt{21}\right)^2}+\sqrt{\left(\sqrt{21}\right)^2-2\cdot3\cdot\sqrt{21}+3^2}\)
\(=\sqrt{\left(7-\sqrt{21}\right)^2}+\sqrt{\left(\sqrt{21}-3\right)^2}\)
\(=\left|7-\sqrt{21}\right|+\left|\sqrt{21}-3\right|\)
\(=7-\sqrt{21}+\sqrt{21}-3\)
\(=4\)
b) \(\left(4+\sqrt{15}\right)\left(\sqrt{10}-\sqrt{6}\right)\sqrt{4-\sqrt{15}}\)
\(=\left[4\cdot\left(\sqrt{10}-\sqrt{6}\right)+\sqrt{15}\cdot\left(\sqrt{10}-\sqrt{6}\right)\right]\cdot\sqrt{4-\sqrt{15}}\)
\(=\left(4\sqrt{10}-4\sqrt{6}+\sqrt{150}-\sqrt{90}\right)\sqrt{4-\sqrt{15}}\)
\(=\left(4\sqrt{10}-4\sqrt{6}+5\sqrt{6}-3\sqrt{10}\right)\sqrt{4-\sqrt{15}}\)
\(=\left(\sqrt{10}+\sqrt{6}\right)\left(\sqrt{4-\sqrt{15}}\right)\)
\(=\sqrt{10\cdot\left(4-\sqrt{15}\right)}+\sqrt{6\cdot\left(4-\sqrt{15}\right)}\)
\(=\sqrt{40-10\sqrt{15}}+\sqrt{24-6\sqrt{15}}\)
\(=\sqrt{5^2-2\cdot5\cdot\sqrt{15}+\left(\sqrt{15}\right)^2}+\sqrt{\left(\sqrt{15}\right)^2-2\cdot3\cdot\sqrt{15}+3^2}\)
\(=\sqrt{\left(5-\sqrt{15}\right)^2}+\sqrt{\left(\sqrt{15}-3\right)^2}\)
\(=\left|5-\sqrt{15}\right|+\left|\sqrt{15}-3\right|\)
\(=5-\sqrt{15}+\sqrt{15}-3\)
\(=2\)
AT
29 tháng 7 2021
câu đầu có \(3-12\sqrt{6}< 0\) nên không căn được nên đề bạn sai
\(\sqrt{31-8\sqrt{15}}+\sqrt{24-6\sqrt{15}}\)
\(=\sqrt{4^2-2.4.\sqrt{15}+\left(\sqrt{15}\right)^2}+\sqrt{\left(\sqrt{15}\right)^2-2.\sqrt{15}.3+3^2}\)
\(=\sqrt{\left(4-\sqrt{15}\right)^2}+\sqrt{\left(\sqrt{15}-3\right)^2}=\left|4-\sqrt{15}\right|+\left|\sqrt{15}-3\right|\)
\(=4-\sqrt{15}+\sqrt{15}-3=1\)
\(\sqrt{49-5\sqrt{96}}-\sqrt{49+5\sqrt{96}}=\sqrt{49-20\sqrt{6}}-\sqrt{49+20\sqrt{6}}\)
\(=\sqrt{5^2-2.5.2\sqrt{6}+\left(2\sqrt{6}\right)^2}-\sqrt{5^2+2.5.4\sqrt{6}+\left(2\sqrt{6}\right)^2}\)
\(=\sqrt{\left(5-2\sqrt{6}\right)^2}-\sqrt{\left(5+2\sqrt{6}\right)^2}=\left|5-2\sqrt{6}\right|-\left|5+2\sqrt{6}\right|\)
\(=5-2\sqrt{6}-5-2\sqrt{6}=-4\sqrt{6}\)
29 tháng 7 2021
\(\sqrt{31-8\sqrt{15}}+\sqrt{24-6\sqrt{15}}\)
\(=4-\sqrt{15}+\sqrt{15}-3\)
=1
2 tháng 7 2021
a) Ta có: \(\left(7\sqrt{48}+3\sqrt{27}-2\sqrt{12}\right)\cdot\sqrt{3}\)
\(=\left(7\cdot4\sqrt{3}+3\cdot3\sqrt{3}-2\cdot2\sqrt{3}\right)\cdot\sqrt{3}\)
\(=33\sqrt{3}\cdot\sqrt{3}\)
=99
b) Ta có: \(\left(12\sqrt{50}-8\sqrt{200}+7\sqrt{450}\right):\sqrt{10}\)
\(=\left(12\cdot5\sqrt{2}-8\cdot10\sqrt{2}+7\cdot15\sqrt{2}\right):\sqrt{10}\)
\(=\dfrac{85\sqrt{2}}{\sqrt{10}}=\dfrac{85}{\sqrt{5}}=17\sqrt{5}\)
c) Ta có: \(\left(2\sqrt{6}-4\sqrt{3}+5\sqrt{2}-\dfrac{1}{4}\sqrt{8}\right)\cdot3\sqrt{6}\)
\(=\left(2\sqrt{6}-4\sqrt{3}+5\sqrt{2}-\dfrac{1}{4}\cdot2\sqrt{2}\right)\cdot3\sqrt{6}\)
\(=\left(2\sqrt{6}-4\sqrt{3}+3\sqrt{2}\right)\cdot3\sqrt{6}\)
\(=36-36\sqrt{2}+18\sqrt{3}\)
d) Ta có: \(3\sqrt{15\sqrt{50}}+5\sqrt{24\sqrt{8}}-4\sqrt{12\sqrt{32}}\)
\(=3\cdot\sqrt{75\sqrt{2}}+5\cdot\sqrt{48\sqrt{2}}-4\sqrt{48\sqrt{2}}\)
\(=3\cdot5\sqrt{2}\cdot\sqrt{\sqrt{2}}+4\sqrt{3}\sqrt{\sqrt{2}}\)
\(=15\sqrt{\sqrt{8}}+4\sqrt{\sqrt{18}}\)
2 tháng 7 2021
a,=\(\left(28\sqrt{3}+9\sqrt{3}-4\sqrt{3}\right).\sqrt{3}\)
\(=28.3+9.3-4.3=99\)
b,\(=\left(60\sqrt{2}-80\sqrt{2}+175\sqrt{2}\right):\sqrt{10}\)
\(=155\sqrt{2}:\sqrt{10}=\dfrac{155}{\sqrt{5}}\)
I
5 tháng 11 2019
=\(\sqrt{9-2.3\sqrt{6}+6}+\sqrt{9+2.3\sqrt{6}+6}\)
=\(\sqrt{\left(3-\sqrt{6}\right)^2}+\sqrt{\left(3+\sqrt{6}\right)^2}\)
=\(\left|3-\sqrt{6}\right|+\left|3+\sqrt{6}\right|\)
=\(3-\sqrt{6}+3+\sqrt{6}\)
=6
CD
0
NT
1
DH
23 tháng 6 2017
\(\dfrac{\sqrt{\sqrt{15}-\sqrt{6}}+\sqrt{\sqrt{15}+\sqrt{6}}}{\sqrt{\sqrt{15}+3}}\)
\(=\dfrac{\sqrt{\sqrt{3}.\left(\sqrt{5}-\sqrt{3}\right)}+\sqrt{\sqrt{3}.\left(\sqrt{5}+\sqrt{3}\right)}}{\sqrt{\sqrt{3}.\left(\sqrt{5}+\sqrt{3}\right)}}\)
\(=\dfrac{\sqrt{\sqrt{3}}.\left[\left(\sqrt{5}-\sqrt{3}\right)+\left(\sqrt{5}+\sqrt{3}\right)\right]}{\sqrt{\sqrt{3}.\left(\sqrt{5}+\sqrt{3}\right)}}\)
\(=\dfrac{\sqrt{5}-\sqrt{3}+\sqrt{5}+\sqrt{3}}{\sqrt{5}+\sqrt{3}}=\dfrac{2\sqrt{5}}{\sqrt{5}+\sqrt{3}}\)
Chúc bạn học tốt!!!
Đặt \(A=\sqrt{15-6\sqrt{6}}+\sqrt{15+6\sqrt{6}}\)
\(\Rightarrow A^2=15-6\sqrt{6}+15+6\sqrt{6}+2\sqrt{\left(15-6\sqrt{6}\right)\left(15+6\sqrt{6}\right)}\)
\(=30+2\sqrt{225-216}=30+2\sqrt{9}=30+6=36\)
\(\Leftrightarrow\orbr{\begin{cases}A=6\\A=-6\end{cases}}\)
Mà \(A>0\)
Suy ra A=6