341] 
ON THE SEXTACTIC POINTS OF A PLANE CURVE. 
257 
or observing that the term multiplied by ^ — is = —(d.V)H, we find 
second line of dffTJ = (- 2Hd® + m$dH) + 7 (-0. V) H). 
Vm—\.y (to — l) 3 v ' ' 
73. For the third line, substituting for V 2 3i7 its value = <&dH — HdQ, we have 
third line of dftJJ = - ($3H - Hd<&). 
74. Hence, uniting the three lines, we have 
dtf, U = -^- 3 (( to-2)279$+ 
+ 
+ 
( -2fi3®+ m*0fl) + ( -^j 5i (-(8.V)ir) 
((2ro - 2) + (- 2TO + 2) <ï>3tf), 
(to —17 
* 2 
(to — 1) 
and, reducing, we have the above-mentioned value of did 3 U.