1)
[tex]f'(x)= \frac{14}{3} x + 4[/tex]
2)
[tex] \frac{14}{3} x + 4 = 0 \\ \frac{14}{3}x = - 4 \\ x = - 4 \times \frac{3}{14 } \\ x = \frac{ - 6}{7} [/tex]
