Angle made by the light ray with the surface of mirror is given as
[tex]\theta_i = 90 - 20 = 70 [/tex]degree
now as we know as per law of reflection that
angle of incidence = angle of reflection
So here we can say that
[tex]\theta_i = \theta_r[/tex]
[tex]\theta_r = 70 degree[/tex]
now the total angle that reflected ray will rotate with respect to incident ray is known as angle of deviation
[tex]\delta =180 - \theta_i - \theta_r[/tex]
[tex]\delta = 180 - 70 - 70 = 40 degree[/tex]
so here reflected light will deviate by total angle of 40 degree fron its incident ray.
