Point form: $a^2$x/x1 + $b^2$y/y1 = $a^2$ + $b^2$ = $c^2$. Note the + sign (contrast with ellipse which has -). Parametric: axcos(theta) + bycot(theta) = $a^2$ + $b^2$. Slope form: y = mx + m$\frac{a^2+b^2}{sqrt}$($a^2$ - $b^2$*$m^2$). From an external point, at most 4 normals can be drawn. The normal at P bisects the angle between the focal radii SP and S'P.