1) $\sqrt{25x²+20x+4}$ $\text{=3}$
⇔$\sqrt{(5x+2)²}$ $\text{=3}$
⇔$\text{l5x+2l}$ $\text{=3}$
⇔$\left[\begin{matrix} 5x+2=-3\\ 5x+2=3\end{matrix}\right.$
⇔$\left[\begin{matrix} 5x=-5\\ 5x=1\end{matrix}\right.$$\left[\begin{matrix} x=-1\\ x=1/5\end{matrix}\right.$
2) $\sqrt{9x²+1-6x}$ $\text{=}$$\sqrt{4x²}$
⇔$\sqrt{9x²-6x+1}$ $\text{=}$$\sqrt{(2x)²}$
⇔$\sqrt{(3x-1)²}$ $\text{=l2xl}$
$\text{Nếu x<0}$
⇒$\text{1-3x= $$-2x}$
⇔$\text{2x-3x= -1}$
⇔$\text{x= -1}$
$\text{Nếu 0}$$\leq$$\text{x}$ $\text{<1/3}$
⇒$\text{1-3x=2x}$
⇔$\text{-5x= -1}$
⇔$\text{x=1/5}$
$\text{Nếu x}$$\geq$ $\text{1/3}$
⇒$\text{3x-1=2x}$
⇔$\text{x=1}$
3)$\sqrt{x²+3x+5}$ $\text{=x+3}$
⇔$(\sqrt{x²+3x+5})²$ $\text{=(x+3)²}$
⇔$\text{x²+3x+5=x+6x+9}$
⇔$\text{3x-6x= -5+9}$
⇔$\text{-3x=4}$
⇔$\text{x= -4/3}$
4) $\sqrt{12+4x}$ $\text{=}$ $\sqrt{9-3x}$
⇔$(\sqrt{12+4x})²$ $\text{=}$ $(\sqrt{9-3x})²$
⇔$\text{12+4x = 9-3x}$
⇔$\text{4x+3x = 9-12}$
⇔$\text{7x = -3}$
⇔$\text{x = -3/7}$
5) $\sqrt{27-9x}$ $\text{+2}$$\sqrt{12-4x}$ $\text{- 3/5}$$\sqrt{75-25x}$ $\text{= 16}$
⇔$\sqrt{9(3-x)}$ $\text{+2}$$\sqrt{4(3-x)}$ $\text{- 3/5}$$\sqrt{25(3-x)}$ $\text{= 16}$
⇔$\text{3}$$\sqrt{3-x}$ $\text{+4}$$\sqrt{3-x}$ $\text{-3}$$\sqrt{3-x}$$\text{ = 16}$
⇔$\text{(3+4-3)}$$\sqrt{3-x}$ $\text{ = 16}$
⇔$4\sqrt{3-x}$ $\text{ = 16}$
⇔$\sqrt{3-x}$ $\text{ = 4}$
⇔$(\sqrt{3-x})$ $\text{= 16}$
⇔$\text{3-x = 16}$
⇔$\text{x = -13}$
