### 11.12.1 The ellipse in the plane: ellipse

See section 12.11.1 for ellipses in space.

The ellipse command draws ellipses and other conic sections.

ellipse can take parameters in different forms.

- ellipse can take one parameter, a second degree equation in the variables x and y (or an expression which will be set to zero).

  ellipse returns and draws the conic section given by the equation.
  Input:

  ellipse(x^2 + 2*y^2 - 1)

  Output:

- ellipse can take three parameters; either three points or two points and a real number. The first two points will be the foci of the ellipse and the third argument will be either a point on the ellipse or the length of the semi-major axis.

  ellipse returns and draws the ellipse.
  Input:

  ellipse(-i,i,i+1)

  Output:

  Input:

  ellipse(-i,i,sqrt(5) - 1)

  Output:

  Note that if the third argument is a point on the real axis, the real affix of the point won’t work, it needs to be specified with the point command.