The equation of tangent at 't' to the PARABOLA `y^(2)=4ax` Atleast one normal to the parabola MUST be real `x^(2)+y^(2)=a^(2)-b^(2)` is called directrix circle of the hyperbola `y=mx+sqrt(a^(2)+bm^(2))` is a tangent to the ellipse `(x^(2))/(a^(2))+(y^(2))/(b^(2))=1`