L.H.S. =
Gemetrical Interpretation
Let O be the point of intersection of diagonals AC and BD of || gm ABCD.
Let
implies that the area of || gm ABCD is twice the area of the || gm whose adjacent sides are semi-diagonals of the first parallelogram.
If are three vectors such that
show that the three vectors
are orthogonal in pairs and
.