The expression given is $9x^2 - y$, which represents a binomial expression with two terms. It is already simplified, but depending on what you're trying to do, it can have different interpretations. Here's a breakdown:

• $9x^2$ is a quadratic term in $x$, representing a parabola if graphed on its own.
• $-y$ is a linear term in $y$.

Possible operations or transformations:

1. If you want to solve for $x$ or $y$, you'll need an equation (e.g., $9x^2 - y = 0$).
2. Graphing the expression would show a 3D surface if you were working in terms of both $x$ and $y$.

Let me know what you'd like to do with this expression!

Would you like to:

1. Solve for a variable in a given equation involving this expression?
2. Factor or simplify it further in any context?
3. Explore how to graph it?
4. See how this expression behaves in calculus (e.g., derivatives or integrals)?
5. Use it in a real-world application?

Tip: Always check whether you are dealing with an equation or just an expression when performing operations.