Answers:
1. Base
2. Function
3. Rational
4. Square
5. Braces
6. Set
7. Empty set
8. Parabolas
9. Directrix
10. Indices
11. Proportion
12. Integer
13. Ratio
14. Digit
15. Coefficient
16. Inverse
17. Ellipse
18. Axiom
19. Matrices