1) Tìm ĐK của x để các căn thức sau có nghĩa:
a) \(\sqrt{x-2}\) b) \(\sqrt{2-3x}\)
2) Tính:
a) (\(\sqrt{8}-3\sqrt{2}\) ). \(\sqrt{2}\) b)\(\dfrac{\sqrt{14}-\sqrt{7}}{1-\sqrt{2}}\)
c) \(\sqrt{4.36}\) d) \(\sqrt{\dfrac{25}{81}.\dfrac{16}{49}}\)
3) Rút gọn:
a) \(\sqrt{19+\sqrt{136}}-\sqrt{19-\sqrt{136}}\) b) \(\sqrt[3]{27}+\sqrt[3]{-64}+2.\sqrt[3]{125}\)
4) Tìm x, biết:
\(\sqrt{4x+20}-2\sqrt{x+5}+\sqrt{9x+45}=6\)
5) Cho :
B = (\(\dfrac{1}{x+2\sqrt{x}}-\dfrac{1}{\sqrt{x}+2}\)) : \(\dfrac{1-\sqrt{x}}{x+4\sqrt{x}+4}\) ( với x > 0; x khác 1)
a) Rút gọn B
b) Tìm x để B = \(\dfrac{5}{2}\)
\(1,\\ a,ĐK:x-2\ge0\Leftrightarrow x\ge2\\ b,ĐK:2-3x\ge0\Leftrightarrow x\le\dfrac{2}{3}\\ 2,\\ a,=\sqrt{16}-3\sqrt{4}=4-6=-2\\ b,=\dfrac{-\sqrt{7}\left(\sqrt{2}-1\right)}{\sqrt{2}-1}=-\sqrt{7}\\ c,=\sqrt{4}\cdot\sqrt{36}=2\cdot6=12\\ d,=\sqrt{\dfrac{25}{81}}\cdot\sqrt{\dfrac{16}{49}}=\dfrac{5}{9}\cdot\dfrac{4}{7}=\dfrac{20}{63}\\ 3,\\ a,=\sqrt{19+2\sqrt{34}}-\sqrt{19-2\sqrt{34}}\\ =\sqrt{\left(\sqrt{17}+\sqrt{2}\right)^2}-\sqrt{\left(\sqrt{17}-\sqrt{2}\right)^2}=\sqrt{17}+\sqrt{2}-\sqrt{17}+\sqrt{2}=2\sqrt{2}\\ b,=3-4+2\cdot5=9\)
\(4,ĐK:x\ge-5\\ PT\Leftrightarrow2\sqrt{x+5}-2\sqrt{x+5}+3\sqrt{x+5}=6\\ \Leftrightarrow\sqrt{x+5}=2\\ \Leftrightarrow x+5=4\Leftrightarrow x=-1\left(tm\right)\\ 5,\\ a,B=\dfrac{1-\sqrt{x}}{\sqrt{x}\left(\sqrt{x}+2\right)}\cdot\dfrac{\left(\sqrt{x}+2\right)^2}{1-\sqrt{x}}=\dfrac{\sqrt{x}+2}{\sqrt{x}}\\ b,B=\dfrac{5}{2}\Leftrightarrow\dfrac{\sqrt{x}+2}{\sqrt{x}}=\dfrac{5}{2}\\ \Leftrightarrow2\sqrt{x}+4=5\sqrt{x}\\ \Leftrightarrow3\sqrt{x}=4\Leftrightarrow\sqrt{x}=\dfrac{4}{3}\Leftrightarrow x=\dfrac{16}{9}\)
