bài `2`
\(a,\sqrt{x^2-4x+4}=5\\ \Leftrightarrow\sqrt{\left(x-2\right)^2}=5\\ \Leftrightarrow x-2=5\\ \Leftrightarrow x=7\)
\(b,\sqrt{4x+20}-3\sqrt{x+5}+\sqrt{16x+80}=15\\ \Leftrightarrow\sqrt{4\left(x+5\right)}-3\sqrt{x+5}+\sqrt{16\left(x+5\right)}=15\\ \Leftrightarrow2\sqrt{x+5}-3\sqrt{x+5}+4\sqrt{x+5}=15\\ \Leftrightarrow3\sqrt{x+5}=15\\ \Leftrightarrow\sqrt{x+5}=5\\ \Leftrightarrow x+5=25\\ \Leftrightarrow x=20\)
Bài `1`
\(a,5\sqrt{\dfrac{1}{5}}+\dfrac{1}{2}\sqrt{20}-\sqrt{45}\\ =\sqrt{\dfrac{25}{5}}+\dfrac{1}{2}\sqrt{4\cdot5}-\sqrt{9\cdot5}\\ =\sqrt{5}+\sqrt{5}-3\sqrt{5}\\ =-\sqrt{5}\)
\(b,\dfrac{2}{2-\sqrt{3}}-\dfrac{1}{2+\sqrt{3}}-3\sqrt{4-2\sqrt{3}}\\ =\dfrac{2\left(2+\sqrt{3}\right)}{4-3}-\dfrac{2-\sqrt{3}}{4-3}-3\sqrt{3-2\sqrt{3}+1}\\ =\left(4+2\sqrt{3}-2+\sqrt{3}\right)-3\sqrt{\left(\sqrt{3}-1\right)^2}\\ =\left(2+3\sqrt{3}\right)-3\left(\sqrt{3}-1\right)\\ =2+\sqrt{3}-3\sqrt{3}+3\\ =5-2\sqrt{3}\)
