SURFACE. 1 17 



II. r, y-V(^-rf). 



29 

 V(<*-<O' 

 ds a a 



A . f ft ax fa c + A 



! *"TS" """"* 



nee in both these examples the centre of gravity is equi- 

 disUnt from the two bounding planes. 



Ex. 3. The surface of a cone. 



- y m SB tan , where a is the semiTertical angle, 



waxt 



ui a sec a dx 3(V-P) 3(A+c) 



Suppose the cycloid 



y - V(2a - ) + a venf 

 to revolve round the axis < 



" 



thus 



Now 



108 



