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Angles of Elevation and Depression

  • If a line of sight is raised through an angle e° from the horizontal, then e° is called an angle of elevation.
  • If a line of sight is lowered through an angle d° from the horizontal, then d° is called an angle of depression.
Examples
  1. A post stands vertically in horizontal ground such that 80 cm of the post is above the ground. Find the length of its shadow when the elevation of the sun is 40°

    • If angle ACB = 40°, then angle CAB = 90° – 40° = 50°
    • BC/AB = tan 50°
    • d/80 = 1.192
    • ⇒ d = 1.192 × 80
    •       = 95.36
    •       = 95 to 2 s.f.
    • ∴ The shadow is 95 cm long.
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