Question

could u plz prove the first law of reflection of light that is angle of incidence is equal to angle of reflection

Answer 1

There is no equation to prove the first law of reflection ,they can be experimentally proved.In the experiment different angles of incidence are taken and the reflected ray is drawn using the plane mirror.With the help of a few observations the first law of reflection is proven.
For more information please check ,Concise physics class IX,chapter 12 ,reflection of light.