Greek letters

3. is the 20th letter of the Greek alphabet. It is used to represent the "u" sound in Ancient Greek
4. it can represent an imaginary unit, similar to the imaginary unit "i" in the complex number system
6. (β) is often used to represent variables, coefficients, or parameters
9. (η) is sometimes used to represent variables, constants, or functions
10. is the 11th letter of the Greek alphabet
12. (ε) it represent a small positive quantity, typically associated with limits, convergence, and approximation
13. it denote the set of all real numbers (the real line) in set theory

1. is frequently used as a variable or parameter
2. is the 18th letter of the Greek alphabet and represents summation
5. is the upper case letter of Θ
7. it is the upper case letter A
8. is the sixth letter of the Greek alphabet and it pronounce as ze-ta
11. it has upper case of (Δ) and it used to change or difference between two values.
13. is the English equivalent of O
14. is the third letter of the Greek alphabet