Cho

- Hướng dẫn giải

$$\begin{gathered} Ta có: {\log }_a\left(x^4{y^2}^{}\right)={\log }_a\left(x^4\right)+{\log }_a\left(y^2\right)=2{\log }_a\left(x^2\right)+2{\log }_a\left(\left|y\right|\right) \to D đúng \\ chú ý : {\log }_a\left(x^2\right)=2{\log }_a\left(\left|x\right|\right) \\ =\left\{\begin{array}{l}2{\log }_a\left(x\right) nếu x\ge 0\\ -2{\log }_a\left(x\right) nếu x<0\end{array}\right. \end{gathered}$$