# Circles and arcs in the plane: circle

### 13.11.1 Circles and arcs in the plane: circle

See also Section 13.11.2.

See Section 14.10 for circles in space.

The circle command creates circles and arcs. You can specify the circle in different ways.

- - circle can take one argument:
    eqn, the equation of a circle with variables x and y (or an expression assumed to be set to 0).
  - circle(eqn) returns and draws the circle.

  #### Example.

  Input:

  circle(x2 + y2 - 2*x - 2*y)

  Output:

- - circle can take two arguments:
    - P, a point.
    - α, a complex number.
  - circle(P,α) returns and draws the circle centered at P and whose radius is |α|.

  #### Example.

  Input:

  circle(-1,i)

  Output:

- - circle can take two arguments:
    A,B, two points (where B must be the value of point and not simply the affix).
  - circle(A,B) returns and draws the circle whose diameter is AB.

  #### Example.

  Input:

  circle(-1,point(i))

  Output:

- - circle can take four mandatory arguments and two optional arguments:
    - C, a point.
    - r, a complex number.
    - a,b, two real numbers.
    - Optionally, var1,var2, variable names.
  - circle(C,r,a,b) returns and draws an arc of the circle with center C and radius |r|, with central angles a and b. The angles start on the axis defined by C and C+r.
    If the arguments var1 and var2 are given, they will be assigned to the ends of the arc.

  #### Examples.

  - Input:
    circle(-1,1,0,pi/4)
    Output:
  - Input:
    circle(-1,point(i),0,pi/4)
    Output: