Therefore, the sum of the other angles of the
quadrilateral is 180° ÐA + ÐQNR = 180°
From the triangle QNR,
r1 + r2 + ÐQNR = 180°
Comparing these two equations, we get
r1 + r2 = A
(9 34)
The total deviation d  is the sum of deviations at the two faces,
d = (i – r1 ) + (e – r2 )
that is,
d  = i + e – A
(9 35)
Thus, the angle of deviation depends on the angle of incidence