Stage: 5 Challenge Level: 
 |
Show that the edges $AD$ and $BC$ of a tetrahedron $ABCD$ are mutually perpendicular when: $AB^2+CD^2 = AC^2+BD^2$. |
Tetrahedra. epsilons. Vector geometry. Vector algebra. Vector notation. Calculating with ratio & proportion. Long problems. Index notation/Indices. Quadratic equations. Pythagoras' theorem.
Published June 1998.
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