1. $\{2\}$

2. $\{1\}$

3. $\left\{-{\displaystyle \frac{2\sqrt{30}}{5}},{\displaystyle \frac{2\sqrt{30}}{5}}\right\}$

4. 6 cm by 9 cm

5. $\{-9,-4\}$

6. $8200

7. 1 in.

8. $\left\{-4,-{\displaystyle \frac{5}{2}}\right\}$

9. ${\displaystyle \frac{1}{9}},{\left(x+{\displaystyle \frac{1}{3}}\right)}^2$

10. $\left\{{\displaystyle \frac{5}{6}}-{\displaystyle \frac{\sqrt{37}}{6}},{\displaystyle \frac{5}{6}}+{\displaystyle \frac{\sqrt{37}}{6}}\right\}$

11. 9 in.

12. $\{-6-\sqrt{3},-6+\sqrt{3}\}$

13. $\{-5,0,5\}$

14. $\{4\}$

15. $\{-12,-6\}$

16. $[90,\infty )$

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

18. $(-\infty ,-2)\cup (5,\infty )$

19. $(-\infty ,2]$

20. $\left[{\displaystyle \frac{2}{5}},2\right]$