3.4․8 Tangents and Normals

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