# Lines and directed lines in the plane: line

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

See Section 14.5.1 for lines in space.

The line command returns and draws a directed line. It can take its arguments in different ways.

Two points:

- line can take two arguments:
  P,Q, two points (which can also be given as a list).
- line(P,Q) returns and draws the line whose direction is from the P to Q.

A point and a slope.

- line can take two arguments:
  - p, a point.
  - slope=m
- line(p,slope=m) returns and draws the line through the given point with the given slope, where direction of the line is determined by the slope.

A point and a direction vector.

- line can take two arguments:
  - P, a point.
  - [u1,u2], a direction vector.
- line(P,[u1,u2]) returns and draws the line through the given point with the direction given by the direction vector.

An equation.

- line can take one argument:
  a*x+b*y+c=0.
- line(a*x+b*y+c=0) returns and draws the line given by the equation. The direction of the line is given by [b,−a].

#### Example.

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) will result in an error.