Find the tangent plane and normal line to the following surfaces at the points shown (see...

Find the tangent plane and normal line to the following surfaces at the points shown (see Problem):

a) z = x2 + y2 at (1, 1, 2),

Problem

Show that the tangent plane at (x1, y1, z1) to a surface given by an equation z = f(x,y) is as follows:

Obtain the equations of the normal line.