To perform the fundamental operation with the functions $f(x) = x^2$ and $g(x) = x - 3$, we generally consider the sum of these functions, denoted as $(f + g)(x)$.

Operation:

$(f + g)(x) = f(x) + g(x)$

Substituting the given functions:

$(f + g)(x) = x^2 + (x - 3)$

Simplifying:

$(f + g)(x) = x^2 + x - 3$

Final Answer:

$(f + g)(x) = x^2 + x - 3$

This is the expression for the sum of the functions $f(x)$ and $g(x)$.

Would you like more details or have any questions? Here are some related questions:

1. How do you perform subtraction of two functions?
2. What happens when you multiply $f(x)$ and $g(x)$?
3. How do you find the composition $f(g(x))$ with these functions?
4. Can you find the derivative of $(f + g)(x)$?
5. What is the domain of the function $(f + g)(x)$?

Tip: When performing operations with functions, always pay attention to combining like terms.