



 
Hi Ben, Here is our diagram. C is the centre of the plante, P is the point where the line of sight is tangent to the planet surface, H is the top of the head of one of the people and r is the radius of the planet. Since triangle HPC is a right triangle Pythagoras' Theorem tell us
Solve for r. Seephen La Rocque and Harley Weston  


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. 