.1 \ i/ ) '//' //;r [Ci. III. 



20. What is the equation of the plane determine. 1 by the line 



2x-3* + y-2 = 0, ar + y + 2+lsO, 

 and the point (5, 2, 6)? 



21. Show analytically that the locus of a point equidistant from t 

 given points is a straight line perpendicular to the plane determin* d 1>\ 

 those three points. 



22. Deri vi equation [17] directly from a figure, without using equa- 

 tion [16]. 







