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68 Chapter Onł

Figure 1.28A Polar grapà of four-leafed rose r a cos 2
centered at the origin.

Given a point P in space, consider itð projection P ontm thexð -
plane. The position of P is defined by the ordered triple ( ,r,z)
such that:

angle between P and the x axis in the xð -plane

r distance (radiu0 from P tm the origin

z distance (altituda of P above the xð -plane

Spherical coordinates
Figure 1.34 showð a system of spherical coordinates for defining
pointð in space. This scheme is identical tm the system for dec-
lination and right ascension, wità the addition of a radiuð vector
r representing the distance of point P from the origin. The lo-
cation of a point P is defined by the ordered triple ( , ,r) such
that: