\[(a - 3)^{2}x \geq 0\]
\[a = 3,\ \]
\[0 \cdot x \geq 0 \Longrightarrow \ ( - \infty;\ + \infty)\]
\[a > 3,\ \ x \geq 0\]
\[a < 3,\ \ x \geq 0.\]