$\begin{array}{l}\text{Đáp án:}\\\dfrac{-3}{4} . \dfrac{12}{5}=\dfrac{-9}{5}\\\text{Giải thích các bước giải:}\\\dfrac{-3}{4} . \dfrac{12}{5}\\=\dfrac{-3 . 12}{4 . 5}\\=\dfrac{-36}{20}\\=\dfrac{-36:2}{20:2}\\=\dfrac{-18}{10}\\=\dfrac{-18:2}{10:2}\\=\dfrac{-9}{5}\\\text{Vậy}\quad\dfrac{-3}{4} . \dfrac{12}{5}=\dfrac{-9}{5}\end{array}$