\[y = 2 \bullet (x - 3)²\]
\[3 \leq x_{1} < x_{2}\]
\[y_{1} - y_{2} =\]
\[= 2 \bullet \left( x_{1} - 3 \right)^{2} - 2 \bullet \left( x_{2} - 3 \right)^{2} =\]
\[= 2 \bullet \left( \left( x_{1} - 3 \right)^{2} - \left( x_{2} - 3 \right)^{2} \right) =\]
\[y_{1} - y_{2} < 0 \Longrightarrow y_{1} < y_{2} \Longrightarrow\]
\[\Longrightarrow y = 2 \bullet (x - 3)^{2}\ возрастает\ \]
\[на\ \lbrack 3; + \infty).\]