\(\displaystyle (AB+CD)^2+(AC-BD)^2=(AB-CD)^2+(AC+BD)^2\)
Is there a name associated with this formula, so that I can find out more about it?
. . their product can be expressed as a sum-of-two-squares in two ways.
. . \(\displaystyle (a^2+b^2)(c^2+d^2) \;=\;\begin{Bmatrix}(ac+bd)^2 + (ad-bc)^2 \\ \\ (ac-bd)^2 + (ad+bc)^2\end{Bmatrix}\)