# Parabola

 A parabola is the locus of a point which moves so that its distances from a fixed point (the locus) and a fixed straight line (the directrix) are the same.  Construct the parabola according to this definition by using the command "perpendicular bisector". Construct the parabola as an envelope of its tangents.
 Construct the pair of tangents from a given point to the parabola. Given a pair of tangents and the focus, construct the parabola.
 Given the focus, a tangent and the point of contact, construct the parabola. Construct a parabola tangent to a fixed circle having a fixed diameter as axis.
 Construct the graph of the quadratic polynomial passing through three given points no two of which have the same abscissa. Construct the graph of the cubic polynomial passing through four given points no two of which have the same abscissa.
 Given coefficients a,b,c,d, construct the graph of the cubic polynomial ax3 + bx2 + cx + d
Generalize the theorem of a chain of four tangential circles to the case of graphs of quadratic polynomials.