a ray of light incident on equilateral glass prism (mui= root 3) moves parallel to the base of prism inside it. what is the angle of incidence of this ray?

In equilateral glass prism , A = 60 degrees . As the ray of light passes symmetrical through the prism, its a minimum deviation position.

Also i = e .. and r = A / 2 ..

hence, r = 30 degrees..

by Snell 's law, Sini / Sinr = n

Sin i / sin30 = n

Sin i = n / 2 .
therefore i = sin inverse of n/2 .. ( n = refractive index = $\sqrt{3}$)
= sin^-1 $\left(\frac{\sqrt{3}}{2}\right)={60}^0$