Hard, pyramid and sphere inscribed

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October 4th 2007, 10:09 AM
Ununuquantium

Hard, pyramid and sphere inscribed

A pyramid $ABCDS$ is given (the base is convex quadrilateral). A sphere is inscribed in this pyramid and it is tangent to side $ABCD$ at point $P$ .
Prove that $\angle APB + \angle CPD = 180^{o}$
October 9th 2007, 06:44 AM
Ununuquantium

Can anybody tell me what are the conditions to inscribe sphere in a such pyramid
October 17th 2007, 08:02 AM
terafull

I remember that base must be circonscrit on a circle. Can anyone confirm?

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