LetAandBbe 2 points on a line andPbe a point off the line. Prove that the shortest distance fromPtoABis given by the following equation:

$\displaystyle d=\frac{\parallel\vec{AP}\times\vec{AB}\parallel}{ \parallel\vec{AB}\parallel}$

I've tried to solve fordusing the Pythagorean theorem and the projection of $\displaystyle \vec{AP}$ onto $\displaystyle \vec{AB}$ for one side and $\displaystyle \vec{AP}$ anddfor the other sides, but I'm stumped.

I can't relate it to the cross product. Can anyone help? Thanks!