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How long is the shadow cast on the ground (represented by the xy-plane) by a pole that is eight meters tall,
given that the sun’s rays are parallel to the vector [5, 3, −2]?
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First, the projection of the given 3D-vector to the (x,y)-plane is the vector V = [5,3].
It defines the direction to the sun in this plane, and its length is | V | = = = .
Next, if the angle of sun rays with the Earth surface (which we interpret as the plane (x,y)) is , then
= .
From the other side, if L is the shadow length, then
= ,
which implies for the shadow length
L = = = = 23.32 meters (rounded). ANSWER
Solved.