[m]=-\frac{32x}{2\sqrt{336-16x^2-16y^2}}=-16\frac{x}{\sqrt{336-16x^2-16y^2}}[/m]
[m]f`_{y}(x;y)=(\sqrt{336-16x^2-16y^2})`_{y}=\frac{1}{2\sqrt{336-16x^2-16y^2}}\cdot (336-16x^2-16y^2)`_{y}=[/m]
[m]=-\frac{32y}{2\sqrt{336-16x^2-16y^2}}=-16\frac{y}{\sqrt{336-16x^2-16y^2}}[/m]
[b]M_(o) (2;-4)[/b]
[m]z_{o}=\sqrt{336-16\cdot (2)^2-16\cdot (-4)^2}=\sqrt{336-64-256}=\sqrt{16}=4[/m]
[m]f`_{x}(M_{o})=-16\frac{2}{\sqrt{336-16\cdot (2)^2-16\cdot (-4)^2}}=-8[/m]
[m]f`_{y}(M_{o})=-16\frac{(-4)}{\sqrt{336-16\cdot (2)^2-16\cdot (-4)^2}}=16[/m]
и подставляем в формулу ( см. рис. 1)
[m]z-4=-8\cdot (x-2)+16\cdot (y-(-4))[/m]
[m]z=-8x+16y+84[/m]