I've been away so I've only just seen this problem. I had a vague memory that the volume of a tetrahedron could be calculated using vector cross and dot products. A quick 'google' took me to this page:

https://math.stackexchange.com/question … ot-product

Your tetrahedron is a regular one by the way which fixes the directions of the vectors IA, IB and IC. So it looks like you can use this formula to get a result. But post back if you need a quick lesson in cross and dot products.

Bob

]]>Find the volume of tetrahedron IA1B1C1 in relation to a.

Sorry, I accidentally cut off half the wording

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