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There is a 10 m tall tower between two parallel roads. The angles of depression of the roads from the top of the tower are 30° and 45° respectively. Approximately, how far are the roads from each other?
30.82 m
27.32 m
29.56 m
26.44 m
27.32 m
For a tower of height h between two roads with angles of depression θ1 and θ2 on opposite sides, the distance between the roads is h(cotθ1+cotθ2)=h(3+1)=10(1.732+1)=27.32 m.
Height of the tower h=10 m, angle of depression of the first road θ1=30°, angle of depression of the second road θ2=45°.
d=h(cotθ1+cotθ2)
For a tower of height h between two roads with angles of depression θ1 and θ2 on opposite sides, the distance between the roads is h(cotθ1+cotθ2)=h(3+1)=10(1.732+1)=27.32 m.
Confusing angles of depression with angles of elevation, or forgetting that the roads are on opposite sides of the tower (summing the distances instead of subtracting them).
Step 1: Understand the Geometry
Let the height of the tower be AB=10 m. Let the two roads be at points C and D on opposite sides of the tower on the ground. The angles of depression from the top of the tower A to roads C and D are 30° and 45° respectively, which means the angles of elevation from the roads to the top of the tower are also 30° and 45°.
h=10 m,θ1=30°,θ2=45°
Step 2: Calculate Distance to the First Road
In right-angled triangle ABC, using the tangent trigonometric ratio: \tan 30°= \frac{AB}{BC} = \frac{10}{BC}BC = \frac{10}{\tan 30° = 10\sqrt{3} \approx 10 \times 1.732 = 17.32\text{ m}
BC=17.32 m
Step 3: Calculate Distance to the Second Road
In right-angled triangle ABD, using the tangent trigonometric ratio: \tan 45°= \frac{AB}{BD} = \frac{10}{BD}BD = \frac{10}{\tan 45° = \frac{10}{1} = 10.00\text{ m}
BD=10.00 m
Step 4: Find Total Distance Between Roads
Since the roads are on opposite sides of the tower, the total distance between the roads is the sum of the two distances BC and D: Total Distance=BC+BD=17.32+10=27.32 m
Total Distance=27.32 m
B is correct because the total distance between the two roads is 103+10≈17.32+10=27.32 m.