### 11.12.3  The parabola in the plane: parabola

See section 12.11.3 for parabolas in space.

The parabola command draws parabolas and other conic sections.

parabola can take parameters in different forms.

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

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

parabola(x^2 - y - 1)

Output:

• parabola can take two parameters, both points. The points will be the focus and vertex of a parabola.

parabola returns and draws the parabola.
Input:

parabola(0,i)

Output:

Note that if the second 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.

• parabola can take two parameters, a point (a,b) and a real number c.

parabola returns and draws the parabola y = b + c(xa)2.
Input:

parabola(-i,1)

Output:

Input:

parabola(-i,i,1/2)

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.