Line perpendicular to given line passing through a point 1. The problem statement, all variables and given/known data What is the vector equation of a line passing through P(1,2,3) which is perpendicular to the line L1 : (x-4)/4 = (y-5)/5 = (z-6)/6 2. Relevant equations Dot product Projections Planes, perhaps? 3. The attempt at a solution I believe I am on the right track but what I'm interested in the other possible ways of tackling this. Since we are given a point on the line in the equation of L1, let's call it Q(4,5,6), I thought I should attempt to project the vector PQ that connects the point on the line with the point P, onto the directional vector of the line. Then, adding the projection, QR, to the original directional vector I should be able to obtain the point on the line, R, where the vector PR is perpendicular to the line L1. From thereon, it's just a matter of using the point R and the vector PR to write out the line's equation. Is my line of thinking correct, and what would be the alternative ways of solving this? The calculus teacher hinted at a number of ways, one of which would involve constructing a plane from the line L1, with the normal of the plane being the vector perpendicular to the line; and the other method having possibly to do with the dot product. I am not sure how one would go about solving this problem in those ways but I am very interested in finding out. Advice much appreciated!