Để 2 đt chia hết
\(\Leftrightarrow3x^3-7x^2+3x-a=\left(3x+2\right)\cdot a\left(x\right)\)
Thay \(x=-\dfrac{2}{3}\)
\(\Leftrightarrow3\cdot\left(-\dfrac{8}{27}\right)-7\cdot\dfrac{4}{9}+3\cdot\left(-\dfrac{2}{3}\right)-a=0\\ \Leftrightarrow\dfrac{-8}{9}-\dfrac{28}{9}-2-a=0\\ \Leftrightarrow-6-a=0\Leftrightarrow a=-6\)