Formula: a = b = c

The formula you mentioned, "a = b = c," is an assignment statement commonly found in programming languages. It is used to assign the same value to multiple variables at once, creating a chain of assignments.

Let's break down how this formula works:

1. First, the value of variable 'c' is determined or already known.

2. Next, this value is assigned to the variable 'b' using the '=' operator. In other words, the value of 'c' is copied into 'b'.

3. Finally, the value of 'b' is assigned to the variable 'a' using the '=' operator. This means that the value of 'b' (and consequently, the value of 'c') is also copied into 'a'.

As a result, all three variables ('a', 'b', and 'c') will hold the same value. Any changes made to one variable will affect the other two, as they are essentially different references to the same value.

Here's an example to demonstrate the formula:

```python
c = 5
a = b = c # assigns the value of 'c' (5) to 'b' and 'a'

print(a) # Output: 5
print(b) # Output: 5
print(c) # Output: 5
```

In this example, 'a', 'b', and 'c' all have the value 5 because of the chain assignment.