(865, #17) Show that the area of the plane z = a x + b y + c that projects onto the region D in the xy-plane with area A(D) is sqrt(1 + a² +b²) A(D).

Solution:The problem asks for the area of the surface z = f(x,y)= a x + b y + c for (x, y) in D.

This area is equal to

by: gm