\[y = 7x² + 5\]
\[x_{1} < x_{2} \leq 0\]
\[y_{1} - y_{2} =\]
\[= \left( 7x_{1}^{2} + 5 \right) - \left( 7x_{2}^{2} + 5 \right) =\]
\[= 7x_{1}^{2} + 5 - 7x_{2}^{2} - 5 =\]
\[= 7 \bullet \left( x_{1}^{2} - x_{2}^{2} \right) =\]
\[y_{1} - y_{2} > 0 \Longrightarrow y_{1} > y_{2} \Longrightarrow y =\]
\[= 7x^{2} + 5\ \ убывает\ на\ ( - \infty;0\rbrack.\]