$a) A(x)=2x-6$
$A(x)=0$
$⇔2x-6=0$
$⇔2x=6$
$⇔x=3$
$b) B(x)=2(x-1)+3(x-x)$
$B(x)=0$
$⇔2(x-1)+3(x-x)=0$
$⇔2x-2=0$
$⇔2x=2$
$⇔x=1$
$c) C(x)=8x^3-2x$
$C(x)=0$
$⇔8x^3-2x=0$
$⇔2x.(4x^2-1)=0$
$⇔$ \(\left[ \begin{array}{l}2x=0\\4x^2-1=0\end{array} \right.\)
$⇔$ \(\left[ \begin{array}{l}x=0\\4x^2=1\end{array} \right.\)
$⇔$ \(\left[ \begin{array}{l}x=0\\x^2=1/4$\end{array} \right.\)
$⇔$ \(\left[ \begin{array}{l}x=0\\x=± 1/2\end{array} \right.\)
