Agh, another thing is that I have to describe the intersection of this equation with this other equation which is a hemisphere (h(x,y) = √ (1-x2 - y2). When I put these two equal to each other f = h i get the equation of

x2 + y2 = 1/5 which is a circle. I can more or less imagine this, ie the cone intersecting the hemisphere at the radius z = 1/5 , where the borders of the cone and hemisphere intersect? Is that right? But then my other question is how can the intersection be 2 dimensional and not 3?

Many thanks again