## Problem:

I am trying to implement the Pythagorean formula in my program using a function. But the program is not running for some reason. I am attaching my code snippet and the error message below:

```
from math import sqrt
def pythagorean (a, b=-1, c):
return sqrt(a ** 2 + c ** 2)
pythagorean(a=3,c=9)
```

Error message:

```
File "main.py", line 17
def pythagorean (a, b=-1, c):
SyntaxError: non-default argument follows default argument
```

As you can see in the error message, **non-default argument follows default argument**. What is this error? How can I fix the error? Thanks for your kind concern buddy.