As the refracted ray passes such that `AQ = AR`, it must go parallel to the base of the prism suffring minimum deviation.
`r = A//2 = (60)/(2) = 30^(@)`
`mu = (sin i)/(sin r)/(sin i)/(sin 30^(@))`
`:. sin I = mu sin 30^(@) = sqrt(3) xx (1)/(2)`
`i = 60^(@)`
As `i + e =A + delta_(m)`
`2i = 60^(@) + delta_(m), delta_(m) = 2 i - 60^(@) = 120^(@) - 60^(@)`
`delta_(m) = 60^(@)`