252 BOOK OF MATHEMATICAL PROBLEMS. 



liMO. If I, ?H, n be the direction cosines of the normal at 

 any point of the conicoid h + = 1, and <j> the angle between 



the geodesic lines through that point and through the umbilici ; 

 then will 



{Pa(c- 

 S <#> ~ZV(6-c) + ... + ... - 2m*n*~bc(a- b)(a- o) - ... - ... ' 



the axis of y being parallel to the circular sections. 



