Final answer:
In mathematics, a reflection over the line y=x is achieved by swapping each point (a, b) to (b, a). The law of reflection pertains to the angle of incidence equaling the angle of reflection and is a concept from physics.
Step-by-step explanation:
The reflection over the line y=x in mathematics involves changing the coordinate positions of a point or figure. In this reflection, each point (a, b) on a shape is transformed into a new point (b, a). Hence, the rule for this reflection is to swap the x-coordinate with the y-coordinate of each point that you're reflecting.
The law of reflection, as used in physics, states that the angle of reflection (θr) equals the angle of incidence (θi). This is primarily related to the behaviour of light or other waves encountering a surface, and although it also involves reflection like in mathematics, it's applied in a different context.