] Tin i\ >/ 



If the chosen c - planes were oblique to M h 



tier, a set of oblique eoOvdiiMlM for any point in naoo 

 gilt U- found MI an entirely analogous way. 

 Unless otherwise stated, rectangular coordinates will be 

 in the subsequent work. 



201. Polar coordinates. A second method of fixing the 

 position of a point in space is by mean** distance and 



dire* ui a givt point. Ixt 



a fixed point in space, called the 

 pole; and let p be the distance from 

 l>oint P. To give the 

 direction of p, let OR and OS be two 

 chosen directed perpendicular lines 

 0, determining the plane 



Him tlu- direction of p will be 

 given l>y the angle 6 from the plane R OS to the plane POM* 

 angle <f> from the line OS to p. Th- ) M iini P is 

 completely determined l>y the values of iu radius vector p 

 and its vector ial angles and fa and may be demoted as 

 P=(/>, ft <f>). The elements p, ft ^ are called the polar 

 coordinates of tho point P. 



It is to be noted that for convenience the positive values 



of and <f> are those for rotation in dockwu* direction from 



V and OS, respectively. And although a given set of 



coordinates fixes a single point, yet any point may have sixteen 



sets of coordinates in a polar system, if, as usual, the values 



10 angles are le** than 800. 



202. Relation between the rectangular and polar systems* 



ixes OR and US of a polar system coincide uith 



axes OX and 02, respect i " a rectangular sys- 



