Find the vector normal to the plane (with positive z-component)? Consider the plane:
x+y+z=D
Find a unit vector normal to the plane with positive z-component.
I am mostly confused by the "positive z-component" statement... How would you find the normal unit vector?

Well, you could find two vectors in the plane and take the cross product to find a normal vector.
Or, more easily, you can use the fact that the coefficients on $x,y,z$ define a normal vector and divide by its magnitude to get a unit vector.
