146 Trans. Acad. Sci. of St. Louis. 



focus, F. If we now let 



<p = <^BFC, we have 



(a 2 -6 2 )* 



= tan <p 



Through the center of the ellipse draw CD parallel to BF; 

 then 



DH = £tan^. 



Figure 5. 

 Through D draw DK perpendicular to CD; then 



HK = DH- tan <p = £ tan 2 <p = 



b 2 



a 2 -b 2 



Z; (22) 



therefore, (eq. 21) the line through K parallel to the axis of 

 Yv& this asymptote. 



To find the asymptote parallel to the axis of X, through 

 the point P draw PQ perpendicular to BF; then 



QH — ?; tan^. 



