$\"\"$

The angle of inclination of the tangent plane :

$\"\"$ , where $\"\"$ is the normal vector.

$\"\"$

The function is $\"\"$ and the point is $\"\"$ .

Consider $\"\"$ .

Gradient of the function $\"\"$ .

$\"\"$ .

Substitute the point $\"\"$ in above equation.

$\"\"$ .

Since the gradient of the function is normal to the surface, $\"\"$ .

Find the angle of inclination of a tangent plane.

$\"\"$

$\"\"$ .

$\"\"$

The angle of inclination of the tangent plane is $\"\"$ .