Size of the angle of incidence?

[Brittykitty]

If the angle between an incident ray and a reflecting surface is 23°, what is the size of the angle of incidence?

Im not quite sure what the formula for this would be, I can't find it in my book :| any help would be very much appreciated. Thank you

 

[cepheid]

By definition, the angle of incidence is measured from the normal to the surface. "Normal" in this context means, "perpendicular." In other words, the normal to a surface is a line that is perpendicular to that surface. Perpendicular, of course, means that it makes a right angle. If the ray makes a 23° angle with the surface itself, what angle does it make with the normal to the surface (which is at a right angle to the surface)? Drawing a picture will really help here.