146 



Trans. Acad. Sci. of St. Louis. 



focus, F. If we now let 



9 



= ^LBFC, we have 



(a 2 -b 2 ) 



r , = tan <f 



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



then 



DH = £ tan <p. 



Figure 5. 

 Through D draw DK perpendicular to CD; then 



HK= DH- tun <p = c tan 2 ^ = ^Ti^ ( 22 ) 



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

 !Fis this asymptote. 



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

 the point P draw PQ perpendicular to BF; then 



QH = T) tan <p. 



