[tex]y = {x}^{2} + 5x + 7 \\y ' = ( {x}^{2} ) '+ (5x)' + 7' = 2x + 5 \\ y' = 0 \\ 2x + 5 = 0 \\ 2x = - 5 \\ x = - 5 \div 2 \\ x = - 2.5[/tex]

Ответ: - 2,5