Given unit vectors L (the direction from a surface point P to a point light source) and N (the unit normal to the surface at P), let R be the direction of specular reflection of the point light at P: R is a unit vector that lies in the plane of L and N such that the angle of reflection is equal to the angle of incidence. Find an expression for R in terms of N and L. Im not quite sure how to approach this at all. any help please?