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Answer:
4) 95.7 m
Step-by-step explanation:
The angle at the cliff base between Alan and Keith is ...
B = 180° -29° -48° = 103°
The law of sines will tell you the distance KB from Keith to the cliff base is
KB/sin(A) = KA/sin(B)
KB = KA×sin(A)/sin(B) = (70 m)sin(29°)/sin(103°) ≈ 34.82935 m
The height of the cliff is found from the tangent relation ...
Tan = Opposite/Adjacent
tan(70°) = height/(34.83 m)
height = (34.83 m)tan(70°) = 95.693 m
The height of the cliff is about 95.7 m.
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Additional comment
These problems can usually be resolved into two 2-D problems. Here, we can work out the distance we need from Keith to the cliff by considering only the ground plan of the site. Then we can work out the height of the cliff only considering the vertical plane containing Keith and the base of the cliff.
The attachment shows the ground plan triangle KAB.
