a)
n = [0, 1, 2] ⨯ [0, 2, 1] = [-3, 0, 0] = -3·[1, 0, 0]
E: (X - [1, 2, 3])·[1, 0, 0] = 0
b)
E: x = 1
S = [2, 1, 0] + r·([3, 1, √3] - [2, 1, 0]) = [1, y, z] → r = -1 ∧ y = 1 ∧ z = -√3 --> S = [1, 1, -√3]
c)
α = ASIN(ABS([1, 0, √3]·[1, 0, 0])/(ABS([1, 0, √3])·ABS([1, 0, 0]))) = 30°