How to find the volume of a tetrahedron - ISEE Upper Level: Quantitative Reasoning

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Question

In three-dimensional space, the four vertices of a tetrahedron - a solid with four faces - have Cartesian coordinates , where .

Give its volume in terms of .

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Answer

A tetrahedron is a triangular pyramid and can be looked at as such.

Three of the vertices - - are on the horizontal plane , and can be seen as the vertices of the triangular base. This triangle, as seen below, is isosceles:

Thingy

Its base is 12 and its height is 15, so its area is

The fourth vertex is off this plane; its perpendicular (vertical) distance to the aforementioned face is the difference between the -coordinates, , so this is the height of the pyramid. The volume of the pyramid is

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