10 questions from actual SSC GD Constable papers · all shown free · click option to reveal solution
When you look up at a tall building, the angle your line of sight makes with the horizontal ground is called the angle of elevation. When you look down from a height, it's called the angle of depression. These angles help us calculate heights and distances we cannot measure directly
The angle of elevation from point A to point B equals the angle of depression from point B to point A. Always draw a right triangle and identify the opposite side, adjacent side, and hypotenuse clearly. The horizontal distance remains constant in most problems.
SSC CGL consistently asks 1-2 questions on this topic. Common scenarios include: tower/building height from given distance, finding distance when height is known, problems involving two angles of elevation, lighthouse/ship problems, and ladder-wall problems.
- ANGLE CHANGE METHOD: When moving closer or farther from an object, use the formula: h = d₁ × tan α = d₂ × tan β, where h is height, d is distance, and α, β are angles. This eliminates the need to calculate height separately.
Draw diagram with tower height = h, man's height = 1.8m, horizontal distance = 150m
Effective height to calculate = h - 1.8m (since man has height)
tan 30° = (h - 1.8)/150
1/√3 = (h - 1.8)/150
h - 1.8 = 150/√3 = 150/1.732 = 86.6m
h = 86.6 + 1.8 = 88.4m WORKED EXAMPLE 2: From a point on ground, a tree top's angle of elevation is 45°. Moving 20m closer, the angle becomes 60°. Find tree height.
Let tree height = h, original distance = d
From original position: tan 45° = h/d, so h = d
From new position: tan 60° = h/(d-20)
√3 = h/(d-20) = d/(d-20) [since h = d]
√3(d-20) = d
1.732d - 34.64 = d
0.732d = 34.64, so d = 47.32m
Tree height h = d = 47.32m
#1: Students forget to account for the observer's height. When a person observes something, always subtract the person's height from the total height calculated. Many students calculate the total vertical distance but forget the observer is not on the ground level. ADDITIONAL SHORTCUTS: For 30-60-90 triangles, use ratio 1:√3:2.
For 45-45-90 triangles, use ratio 1:1:√2. When angle of elevation doubles, use the identity tan(2θ) = 2tan(θ)/(1-tan²θ). Remember that complementary angles have reciprocal trigonometric ratios.
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