30 SCIENCE ABSOLUTE OP SPACE. 



^=X(X 2 -l), and 



=X 2 (X 2 -1), whence, by inte- 

 ctx 



gration, we get (as in 30) 



^=^(X 8 -l)*=*cot CBN. 

 III. Manfestly 



dx dx 



which (unless given in y) now first is to be ex- 

 pressed in terms of y; whence we get u by 

 integrating. 



D If AB=/, AC=?, CD=r, and 

 CABDC=s/ we might show (as 

 in II) that 



-= =r, which = 



FIG. 25. aq 



and, integrating, s=%pi ^f_ ~f 



This can also be deduced apart from inte- 

 gration. 



For example, the equation of the circle (from 

 31, III), of the straight (from 31, II), of a 

 conic (by what precedes), being expressed, the 



