3.4․8 Tangents and normals

Condition: Find the tangent plane and the normal to the surface \( z=5 x^{2}+2 x y+\tan ^{-1} \frac{x}{y} \) at the point of intersection of the planes \( x+y+2 z=1 \), \( x+2 y=1, x+z=0 \)