a: \(2x^2\cdot\sqrt{\frac{9}{4x^6}}=2x^2\cdot\frac{3}{2\cdot\left(-x^3\right)}\) (do x<0)
\(=\frac{6x^2}{-2x^3}=\frac{-3}{x}\)
b: \(\frac{x}{8y^2}\cdot\sqrt{\frac{144y^6}{x^2}}=\frac{x}{8y^2}\cdot\frac{12\cdot\left|y^3\right|}{x}\) (do x>0)
\(=\frac{-12y^3}{8y^2}\) (do y<0)
\(=-\frac32y\)