Angle of depression
- CBSE · NCERT Class 10, Ch 9 Some Applications of Trigonometry
The angle of depression is the angle between the horizontal and the line of sight when you look down at something below your eye level.
You stand on a cliff and lower your head to see a boat. The angle is measured down from the flat line at your eye, not from the upright cliff. The angle of depression from you to the boat equals the angle of elevation from the boat to you. The two flat lines are parallel, so the angles match.
A small example
From the top of a 30 m cliff, a boat is seen at an angle of depression of 30°. At the boat, the angle up to the cliff top is also 30°. So tan 30° = 30 ÷ distance. Since tan 30° = 1/√3, the distance is 30√3 m, about 52 m.
Where marks go
Question 35(B) of CBSE's 2026-27 Maths Standard sample paper uses angles of depression of 45° and 30° to two ships. In the 2026-27 Maths Standard marking scheme, the figure earns 1 mark. Each tan equation earns 1 mark, and each step that follows earns its own half or whole mark.
Since the figure has its own mark, draw it first and mark the angle down from the horizontal at the eye. Reading which angle the labels mark comes before any formula.
Sources
Facts last checked against these sources on 30 September 2026.
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