WAEC 2018 Mathematics · Question 13
The angle of elevation of the top of a tree from a point 27m away and on the same horizontal ground as the…
Question
The angle of elevation of the top of a tree from a point 27m away and on the same horizontal ground as the foot of the tree is 30. Find the height of the tree.
- A.27m
- B.13.5
- C.13.5
- D.9
Answer: D. 9
Explanation written with AI and checked against the answer key
Analyze the question: The tree stands vertically on level ground. You are 27 m from its foot, and the angle of elevation of its top is 30°. This forms a right-angled triangle:
- Adjacent side (ground distance) = 27 m
- Opposite side (tree height) = h
- Angle = 30°
Concept: When you know the adjacent and want the opposite, use tangent:
tan θ = opposite / adjacent
Solution:
tan 30° = h / 27
Since tan 30° = 1/√3:
h = 27 / √3
Rationalise by multiplying top and bottom by √3:
h = 27√3 / 3 = 9√3 m
Check against the options:
- A. 27 m: this would need a 45° angle, so it is wrong.
- B. 13.5√3 m ≈ 23.4 m: too large.
- C. 13.5√2 m: not related to 30°.
- D. 9√3 m ≈ 15.6 m: matches (27 × 0.5774 ≈ 15.59).
Tip: Memorise the tan values: tan 30° = 1/√3, tan 45° = 1, tan 60° = √3. With 30° and a distance that is a multiple of 3, the answer is usually a "something√3" after rationalising. Remember SOH-CAH-TOA: here the sides involved are Opposite and Adjacent, so use TOA.
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