While there isn't a strict rule about the "three parts" of a formula, we can think of it in terms of three key elements that are often present:

1. Operator(s): This is the "action" of the formula. It tells you what to do with the other elements. Common operators include:

* Arithmetic operators: +, -, *, /, ^ (addition, subtraction, multiplication, division, exponentiation)

* Logical operators: =, <, >, <=, >=, != (equal to, less than, greater than, less than or equal to, greater than or equal to, not equal to)

* Special functions: SUM, AVERAGE, IF, etc.

2. Operands: These are the values the operator acts upon. They can be:

* Numbers: 10, 2.5, -3.14

* Cell references: A1, B2, C3 (referring to specific cells in a spreadsheet)

* Text strings: "Hello", "World"

* Other formulas: If a formula itself is used as an operand in another formula.

3. Parentheses: Used to define the order of operations. Calculations within parentheses are performed before those outside of them.

Example:

* Formula: `=SUM(A1:A5) * 2`

* Operator: `SUM` (function) and `*` (multiplication)

* Operands: `A1:A5` (cell range) and `2` (number)

* Parentheses: `SUM(A1:A5)` (defines the range to sum)

Remember that formulas can have more than three parts, and the specific elements will vary depending on the formula's purpose.