Direction vector: the direction of a straight line in space is represented by a non-zero vector parallel to the straight line, which is called the direction vector of the straight line.

Solution of direction vector

So as long as a straight line is given, two direction vectors can be constructed (starting from the origin).

That is to say, given a straight line l:ax+by+c=0, the direction vector of the straight line L is

S=(-b, a) or (b, -a).

If the slope of the straight line L is k, then a direction vector of L is?

s=( 1，k)

If a (x 1, y 1) and b (x2, y2), a direction vector of the straight line where AB is located.

s=(x2-x 1，y2-y 1)