Given is a regular n-sided pyramid with top T and base A1A2A3...An. The line perpendicular to the ground plane through a point B of the ground plane within A1A2A3...An intersects the plane TA1A2 at C1, the plane TA2A3 at C2, and so on, and finally the plane TAnA1 at Cn. Prove that BC1+BC2+...+BCn is independent of choice of B's. geometryfixed3D geometrypyramid