Đáp án:

Giải thích các bước giải:

$ a) \ 2\sqrt{54} -\dfrac{2}{5}\sqrt{150} -3\sqrt{24} =2\sqrt{9.6} -\dfrac{1}{5}\sqrt{25.6} -3.\sqrt{4.6}\\ =2.3\sqrt{6} -\dfrac{1}{5} .5\sqrt{6} -3.2\sqrt{6} =-\sqrt{6}\\ b) \ \left(\sqrt{99} -\sqrt{18} -\sqrt{11}\right)\sqrt{11} +3\sqrt{22}\\ =\left(\sqrt{9.11} -\sqrt{9.2} -\sqrt{11}\right)\sqrt{11} +3\sqrt{22}\\ =\left( 3\sqrt{11} -3\sqrt{2} -\sqrt{11}\right)\sqrt{11} +3\sqrt{22}\\ =\left( 2\sqrt{11} -3\sqrt{2}\right)\sqrt{11} +3\sqrt{22} =2.11-3\sqrt{22} +3\sqrt{22} =22\\ Bài\ 2:\ \\ a) \ \sqrt{9x^{2}} =18 \rightarrow 3|x|=18 \rightarrow |x|=6\ \\ \rightarrow \left[ \begin{array}{l l} x=6 & \\ x=-6 & \end{array} \right.\\ b) \ \sqrt{4x^{2} -12x+9} =7 \rightarrow \sqrt{( 2x-3)^{2}} =7 \rightarrow |2x-3|=7\\ \rightarrow \left[ \begin{array}{l l} 2x-3=7 & \\ 2x-3=-7 & \end{array} \right.\rightarrow \left[ \begin{array}{l l} x=5 & \\ x=-2\ & \end{array} \right.$

chúc bẹn học tốt :>

$\displaystyle \begin{array}{{>{\displaystyle}l}} a) \ 2\sqrt{54} -\frac{2}{5}\sqrt{150} -3\sqrt{24}\\ =2\sqrt{9.6} -\frac{1}{5}\sqrt{25.6} -3.\sqrt{4.6}\\ =2.3\sqrt{6} -\frac{1}{5} .5\sqrt{6} -3.2\sqrt{6}\\ =-\sqrt{6}\\ b) \ \left(\sqrt{99} -\sqrt{18} -\sqrt{11}\right)\sqrt{11} +3\sqrt{22}\\ =\left(\sqrt{9.11} -\sqrt{9.2} -\sqrt{11}\right)\sqrt{11} +3\sqrt{22}\\ =\left( 3\sqrt{11} -3\sqrt{2} -\sqrt{11}\right)\sqrt{11} +3\sqrt{22}\\ =\left( 2\sqrt{11} -3\sqrt{2}\right)\sqrt{11} +3\sqrt{22}\\ =2.11-3\sqrt{22} +3\sqrt{22}\\ =22\\ Bài\ 2:\ \\ a) \ \sqrt{9x^{2}} =18\\ \rightarrow 3|x|=18\\ \rightarrow |x|=6\ \\ \rightarrow \left[ \begin{array}{l l} x=6 & \\ x=-6 & \end{array} \right.\\ b) \ \sqrt{4x^{2} -12x+9} =7\\ \rightarrow \sqrt{( 2x-3)^{2}} =7\\ \rightarrow |2x-3|=7\\ \rightarrow \left[ \begin{array}{l l} 2x-3=7 & \\ 2x-3=-7 & \end{array} \right.\rightarrow \left[ \begin{array}{l l} x=5 & \\ x=-2\ & \end{array} \right. \end{array}$