I was looking at the following graph here, and regarding the sets of two functions' given at:
(i)$\,\,\,\,\,$#4,5 given as: $y= \tan a.x \{0<x<cos a\}, \,\, y= \tan a.x \{cos a<x<0\}$;
(ii)$\,\,$ #6,7 given as: $x = \cos(a)\{0<y<\sin(a)\}, \,\, x = \cos(a)\{\sin(a)<y<0\}$;
(iii)#10,11 given as: $y = 0\{0< x < \cos a\},\,\, y = 0\{\cos a< x < 0\}$.
This is causing confusion, & want to know the significance of the bounds given.
I mean that why two separate intervals are given rather than, say replacing the bounds given at:
(i) $\,\,\,\,$#4,5 by a single one as: $y= \tan a.x \{-cosa<x<cos a\}$;
(ii) $\,$ #6,7 by simply one as : $x = \cos(a)\{-\sin(a)<y<\sin(a)\}$;
(iii) #10, 11 by a single one as : $y = 0\{-\cos a< x < \cos a\}$.