explain this concept: Position Vector: Any point on the sphere can be described by a position vector r ( u , v ) r (u,v) in terms of u u and v v: r ( u , v ) = [ A sin ( u ) cos ( v ) A sin ( u ) sin ( v ) A cos ( u ) ] r (u,v)=[ Asin(u)cos(v) Asin(u)sin(v) Acos(u) ] Here, A A is the radius of the sphere. Calculating the Surface Area