a: Đặt A(x)=0
=>(x+3)(x-1)=0
=>\(\left[{}\begin{matrix}x+3=0\\x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=1\end{matrix}\right.\)
b: Đặt B(x)=0
=>\(5x-3x^2=0\)
=>x(5-3x)=0
=>\(\left[{}\begin{matrix}x=0\\5-3x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{5}{3}\end{matrix}\right.\)