For the case shown in figure shown in figure prove the relations `r' - r = A` and `delta = 1 (i-e) + A` (do not try these relations because the prism is normally not used on this way).

Explanation

In `Delta PQR`,
`A + /_PQR + /_QRP = 180^(@)`
`= A + r + 90^(@) -r' = 180^(@)`
`:. R^(1) - r = A`
Deviation after `I^(st)` refraction
`delta_(1) = (i-r)` (anticlock wise)
Deviation after `II^(nd)` refraction
`delta_(1) = (i-r)` (anti clock wise)
Deviation after `II^(nd)` refraction
`delta_(2) = (theta-r') (clock wise)
Hence met devoatopm
`delta = delta_(1) - delta_(2)`
`= (i-r) - (e-r') = i - theta + A`