Find the distance between the directrices of the hyperbola x29−y24=1\frac{x^2}{9} - \frac{y^2}{4} = 19x2−4y2=1.
1813\frac{18}{\sqrt{13}}1318
181313\frac{18\sqrt{13}}{13}131813
91313\frac{9\sqrt{13}}{13}13913
13\sqrt{13}13