v 4.15
E
∥
r
0
E
∥
i
0
=
−
N
2
12
cos
α
−
√
N
2
21
−
sin
2
α
N
2
12
cos
α
+
√
N
2
21
−
sin
2
α
E
r
0
∥
E
i
0
∥
=
−
N
12
2
cos
α
−
N
21
2
−
sin
2
α
N
12
2
cos
α
+
N
21
2
−
sin
2
α
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