# Maths - Projections of lines on planes - Forum Discussion

 By: Nobody/Anonymous - nobody Correction on Projections of lines on planes   2004-05-21 12:56 Here: https://www.euclideanspace.com/maths/geometry/elements/plane/lineOnPlane/ It is stated that: "So the direction is: (A x B) x B" It should be: B x (A x B) or: (B x A) x B (B x A) is indeed out of the page as the text says but (A x B) x B has opposite direction to A || B. I've also tried to implement the "Alternative using Matrix representation" without success. Since I'm pressed for time, I didn't try to find out why.
 By: Martin Baker - martinbaker RE: Correction on Projections of lines on planes   2004-05-24 16:18 Thanks very much for this, Im away from my main computer at the moment but as soon as I get back I will work through this and update the webpage. Martin
 By: Martin Baker - martinbaker RE: Correction on Projections of lines on planes   2004-06-07 14:58 Thanks very much, I have updated the page now. Sorry it took so long but I underestimated all the work waiting for me when I got back to base. Martin
 By: Nobody/Anonymous - nobody RE: Correction on Projections of lines ...   2004-09-01 14:12 Hello, Some typos : paragraph : Calculation of the projection on the plane But from this page we know that: ... _ _ _ A || B = |A| xB x A x B <- unit vectors A,B should be separated ? paragraph : Calculation of the perpendicular component Therefore combining these equations gives: A | B <- instead of A || B --- grouping terms, Alternative using Matrix representation (A B)x = (Az * Bx* Bz - Bz * Ax* Bz - @ Ax * By* By + Bx * Ay* By) / (Bx2 + By2 + Bz2) @ missing a minus sign here Thanks for popularizing so complex stuffs ! Nop
 By: Martin Baker - martinbaker RE: Correction on Projections of lines on pla   2004-09-02 14:09 Thanks very much, I have fixed this page as you suggested. Martin