Where should the spotlight be placed ?

Geometry Level pending

A spotlight projects a cone of light of semi-vertical angle 2 0 20^{\circ} . A Cartesian coordinate system is chosen such that the stage is coincident with the horizontal x y xy plane. We want the spotlight to generate a light spot on the stage that is an ellipse centered at ( 20 , 20 , 0 ) (20, 20, 0) , has a semi-major axis length of 10 10 and a semi-minor axis length of 5 5 , such that the major axis makes a counter clockwise angle with the x-axis of 3 0 30^{\circ} . Where should the spotlight be placed ? If it is to be placed at P ( x , y , z ) P(x, y, z) , where x > 20 x \gt 20 , y > 20 y \gt 20 and z > 0 z \gt 0 , and if the splotlight axis direction (towards the stage) in the x y z xyz coordinate frame is along the unit vector u = ( u x , u y , u z ) \mathbf{u} = ( u_x , u_y, u_z ) , then find x + y + z + 10 ( u x + u y + u z ) x + y + z + 10(u_x + u_y + u_z )


The answer is 50.04.

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