What is geometrical significance of the relation `|veca+vecb|` = `|veca-vecb|`

Explanation

Let ABCD be a parallelogram where `vec(AB) = veca, vec(BC) = vecb`
Then `vec(AC) = veca+vecb`
Again `vec(AD) = vecb`
So `vec(DB) = veca-vecb`
Now AC = `|vec(AC)| = |veca+vecb|`
DB = `|vec(DB)| = |veca-vecb|`
If `|veca+vecb| = |veca-vecb|` then AC = DB.
Thus ABCD is a parallelogram where two diagonals are equal.
Hence ABCD must be a tectangle with adjacent vectors `veca` and `vecb`.