1. $\{(-1,2)\}$

3. $\varnothing$

5. $\{(2,3)\}$

7. $\{(1,-1,2)\}$

9. $\{(-1,2,-3)\}$

11. $\varnothing$

13. $\{x,2x-8,11-3x\}$

15. $\varnothing$

17. $\left({\displaystyle \frac{7}{3}}-{\displaystyle \frac{2}{3}}z,{\displaystyle \frac{2}{3}}-{\displaystyle \frac{1}{3}}z,z\right)$

19.

21.

23.

25. Max of 14 at $x=7,y=0$

27. Min of $-9$ at $x=0,y=-3$

29. $\left\{(-2,1),\left({\displaystyle \frac{8}{3}},-{\displaystyle \frac{5}{9}}\right)\right\}$

31. $\left\{(2,-2),\left(-{\displaystyle \frac{2}{3}},-{\displaystyle \frac{14}{3}}\right)\right\}$

33. $\left\{(1,2),(-1,-2),\left(2\sqrt{2},{\displaystyle \frac{\sqrt{2}}{2}}\right),\left(-2\sqrt{2},-{\displaystyle \frac{\sqrt{2}}{2}}\right)\right\}$

35.

37.

39.

41. ${\displaystyle \frac{2}{x+2}}-{\displaystyle \frac{1}{x+3}}$

43. ${\displaystyle \frac{2}{x-1}}+{\displaystyle \frac{1}{x}}+{\displaystyle \frac{5}{{(x-1)}^2}}$

45. ${\displaystyle \frac{-1+2x}{{(x^2+4)}^2}}+{\displaystyle \frac{1}{x^2+4}}$