#)Giải :
\(x^2y^2.\sqrt{\frac{9}{x^2y^4}}=x^2y^2.\frac{3}{xy^2}=3x\)
\(x^2y^2\sqrt{\frac{9}{x^2y^4}}\)
\(=x^2y^2\sqrt{\frac{3^2}{\left(xy^2\right)^2}}\)
\(=\frac{3x^2y^2}{xy^2}\)
\(=3x\)
Ta có : \(x^2y^2\sqrt{\frac{9}{x^2y^4}}=x^2y^2\sqrt{\left(\frac{3}{xy^2}\right)^2}=x^2y^2\left|\frac{3}{xy^2}\right|\)( 1 )
x \(\ge\) 0 thì ( 1 ) trở thành : \(x^2y^2.\frac{3}{xy^2}=3x\)
x < 0 thì ( 1 ) trở thành : \(x^2y^2.\frac{3}{-xy^2}=-3x\)