From the figure, we can deduce that the magnitude of α is limited to 0° ≤ "α" < 90°. On the contrary, the vector b × c may form with a an internal angle "β" larger than 90° (0° ≤ "β" ≤ 180°). Namely, since b × c is parallel to "h", the value of "β" is either "β" = "α" or "β" = 180° − "α". So 