Law of reflection:angle of incidence= angle of reflection This formula is only used when the angles are measured from the normal to the ray and not from the ray to the mirror. In this diagram we see that the angle is measured from the ray to the mirrot .The normal measures 90° so we need to subtract 90° from 35° to get the angle of incidence which is 55° . We now that angle of incidence= Angle of reflection hence the answer will be 55°