Curved Surface Area & Total Surface Area of a Pyramid
The angle opp...
Question
The angle opposite to the base edge of a square pyramid on its lateral face is 30∘. If the slant height of the pyramid is 20cm, what is the lateral surface area of the pyramid? (Note that tan15∘=0.268)
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Solution
Since the triangular face of a pyramid is isosceles, we have AC bisecting BD. Thus, using trigonometric ratios in △ACD where ∠CAD=∠BAD2=15∘, we have tan15∘=CDAC=CD20 ⟹0.268=CD20 ⟹CD=0.268×20=5.36cm⟹Baseedge=2×5.36cm=10.72cm[1mark]
Thus, Area of △ABD=12×10.72×20=107.2cm2
Now, the lateral surface area of the pyramid = 4×Areaofthe△ABD
= 4×107.2=428.8cm2[1mark]