P(m,n),Q(m,-n)
A1P:y=n/(m+3)*(x+3)
A2Q:y=-n/(m-3)*(x-3)
两线交点为(9/m,3n/m)
因为P在双曲线上m^2/9-n^2/4=2
所以8x^2+9y^2=36