Show that `(vecaxxvecb)^2 = a^2b^2 - (veca.vecb)^2`.

Explanation

`vecaxxvecb = ab sinthetahatn`
Where a = `|veca|, b = |vecb|` = `theta` is the angle between two vectors `veca` and `vecb` and `hatn` is the unit vector perpendicular to `veca.vecb`.
Now `(vecaxxvecb)^2 = (vecaxxvecb).(vecaxxvecb)
= `a^2b^2 sin^2 theta (hatn.hatn)`
= `a^2 b^2 sin^2 theta = a^2b^2- a^2b^2 cos^2 theta`.
= `a^2b^2-(abcostheta)^2 = a^2b^2-(veca.vecb)^2`. (Proved)