The hyperbolas \[\frac{x^2}{4} - \frac{y^2}{9} = 1\]and \[\frac{y^2}{18} - \frac{x^2}{N} = 1\]have the same asymptotes. Find $N.$
I know that the asymptotes of a hyperbola of the form \[\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1\]are the lines \[y = \pm \frac{b}{a} x.\] So, for the first hyperbola, the asymptotes are \[y = \pm \frac{3}{2} x.\] For the second hyperbola, the asymptotes are \[y = \pm \frac{\sqrt{18}}{\sqrt{N}} x.\] Since the asymptotes are the same, I can equate the slopes and get \[\frac{3}{2} = \frac{\sqrt{18}}{\sqrt{N}}.\] Squaring both sides, I get \[\frac{9}{4} = \frac{18}{N}.\] Multiplying both sides by $N$, I get \[9N = 72.\] Dividing both sides by 9, I get \[N = 8.\] 