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#1 Re: Help Me ! » 3-dimention » 2011-12-24 23:40:48

hi,

i'm arieneytio... try to imagine the equilateral triangle base of the pyramid..

then the measure of one of its side is a. using special angle trigonometry, we can solve that the perpendicular distance from the side of the triangular base to the incenter(or the projection of the tip of the pyramid) will be "a(sqr.rt of 3)/4".

forming a right triangle with the height of the pyramid h and base "a(sqr.rt3)/4", we can now use tangent function to get the angle between the two plane.

angle= arc tan [4h/a(sqr.rt of 3)]

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