19. a) y = x² −4x+1; б) y = -10/x; в) y=1/3x-4.

19. a) $$y = x^2 - 4x + 1$$

б) $$y = -\frac{10}{x}$$

в) $$y = \frac{1}{3}x - 4$$

Ответ: $$y = x^2 - 4x + 1$$, $$y = -\frac{10}{x}$$, $$y = \frac{1}{3}x - 4$$