13.12.3  The parabola in the plane: parabola

See Section 14.11.3 for parabolas in space.

The parabola command draws parabolas and other conic sections. parabola can take parameters in different forms.

• • parabola can take one argument:
    eqn, a second degree equation in the variables x and y (or an expression which will be set to zero).
  • parabola(eqn) returns and draws the conic section given by the equation eqn.

  
  

  Example.
  Input:

  parabola(x^2 - y - 1)

  Output:

  
• • parabola can take two arguments:
    F,V, two points.
  • parabola(F,V) returns and draws the parabola with focus F and vertex V.

  
  

  Example.
  Input:

  parabola(0,i)

  Output:

  
• • parabola can take two parameters:
    • A=(a,b), a point.
    • c, a real number.
  • parabola(A,c) returns and draws the parabola y = b + c(x − a)².

  
  

  Examples.

  • Input:
    parabola(-i,1)
    Output:
    
  • Input:
    parabola(-i,i,1/2)
    Output: