# Thread: Equation of a line

1. ## Equation of a line

Find the Cartesian form of the equation of the straight line l1 which passes through the point p=(2,3,0) and q=(0,1.2).
Find also the Cartesian form of the equation of a straight line l2 which passes through p, is perpendicular to l1 and parallel to the plane Oxy.

I have done the first part by using the equation of a straight line passing from two points, but for part b I don't know how to deduce it. Any help would be appreciated!

2. Hint : The line $l_2$ is in the direction of $\vec{pq}\times (0,0,1)$.

3. So the equation of my line would be p+t(pq x (0,0,1)), where p is my point, t is a parameter and pq x (0,0,1) is the cross product between pq and (0,0,1) which in my case is the direction of the line? Thanks you!

4. Originally Posted by Darkprince
So the equation of my line would be p+t(pq x (0,0,1)), where p is my point, t is a parameter and pq x (0,0,1) is the cross product between pq and (0,0,1) which in my case is the direction of the line?

Right.

5. Thank you!