\(y=f(x)=\dfrac{4}{3}x+4\\a)f(-2)=\dfrac{4}{3}.(-2)+4\\\quad\quad\quad=\dfrac{4}{3}.\\+)f\left(\dfrac{3}{4}\right)=\dfrac{4}{3}.\dfrac{3}{4}+4\\\quad\quad\quad\quad=5.\\+)f(6)=\dfrac{4}{3}.6+4\\\quad\quad\quad=12.\\\text{Vậy }f(-2)=\dfrac{4}{3};f\left(\dfrac{3}{4}\right)=5;f(6)=12.\\b)\text{Để }y=-2\\\Leftrightarrow \dfrac{4}{3}x+4=-2\\\Leftrightarrow \dfrac{4}{3}x=-6\\\Leftrightarrow x=-\dfrac{9}{2}.\\\text{Vậy với }x=-\dfrac{9}{2}\text{ thì }y=-2.\)
