\(1,\sqrt{18x}\cdot\sqrt{8x}\\ =\sqrt{18x\cdot8x}\\ =\sqrt{144x^2}\\ =\left|12x\right|\\ =12x\left(x>0\right)\\ 2,\sqrt{6y}\cdot\sqrt{24y}\\ =\sqrt{6y\cdot24y}\\ =\sqrt{144y^2}\\ =\left|12y\right|\\ =-12y\left(y\le0\right)\\ 3,\sqrt{75\left(x-18\right)^2}\\ =\sqrt{\left[5\sqrt{3}\left(x-18\right)\right]^2}\\ =\left|5\sqrt{3}\left(x-18\right)\right|\\ =5\sqrt{3}\left(x-18\right)\left(x>18\right)\)
`5)` \(\sqrt{75\left(x-18\right)^2}\)
\(=\sqrt{75}.\left|x-18\right|\)
Mà \(x\le-12\Rightarrow x-18\le-30< 0\)
\(\Rightarrow\left|x-18\right|=18-x\)
\(=\sqrt{75}.\left(18-x\right)\)
`6)` \(\sqrt{180\left(x-7\right)^2}\)
\(=\sqrt{180}.\left|x-7\right|\)
Mà \(x< 7\Rightarrow x-7< 0\Rightarrow\left|x-7\right|=7-x\)
\(=6\sqrt{5}.\left(7-x\right)\)
