Bài 1
a) A có nghĩa khi \(\dfrac{-3}{3-x}>0< =>3-x>0< =>x>3\)
b) B có nghĩa khi \(x+\dfrac{1}{x}>0=x>0\)
Bài 2
a) \(M=\left(\sqrt{2}-\sqrt{3-\sqrt{5}}\right)\sqrt{2}+\sqrt{20}\)
\(=2-\sqrt{\left(\sqrt{5}-1\right)^2}+2\sqrt{5}\)
\(=2-\sqrt{5}+1+2\sqrt{5}\)
\(=\sqrt{5}+3\)
b) \(N=\left(\dfrac{\sqrt{6}+\sqrt{2}}{1-\sqrt{3}}-\dfrac{5}{\sqrt{5}}\right):\dfrac{1}{\sqrt{5}-\sqrt{2}}\)
\(=\left(\dfrac{\sqrt{2}\left(\sqrt{3}-1\right)}{1-\sqrt{3}}-\sqrt{5}\right).\left(\sqrt{5}-\sqrt{2}\right)\)
\(=-\left(\sqrt{5}+\sqrt{2}\right)\left(\sqrt{5}-\sqrt{2}\right)\)
\(=-3\)
Câu 1
a: ĐKXĐ: -3/3-x>=0
=>3-x<0
hay x>3
b: ĐKXĐ: x+1/x>=0
=>x>0
