### 12.7.1 Lines and directed lines in the plane: line

See section 13.5.1 for lines in space.

The line command returns and draws a directed line given one of the following types of arguments:

- Two points or a list of two points.
  The direction of the line is from the first point to the second point.
- A point and a slope given by slope=value.
  The direction of the line is determined by the slope.
- A point and direction vector (in the form [u1,u2]).
  The direction of the line is given by the direction vector.
- An equation of the form a*x+b*y+c=0.
  The direction of the line is given by [b,-a].

Input:

line(0,1+i)

or:

line(1+i,slope=1)

or:

line(1+i,[3,3])

or:

line(y - x = 0)

Output:

Warning: To draw a line with an additional argument for color (such as color = blue), this argument must be the third argument. In particular, for a list of two points to specify a line in this command, the list must be turned into a sequence, such as with op. For example, given a list L of two points (possibly the result of a different command) which determines a line, to draw the line blue enter line(op(L),color=blue); entering line(L,color=blue) results in an error.