The expression you've provided is:

$Z = x^3 - 5xy + 5y^2 + 7x - 15y$

This is a multivariable function involving both $x$ and $y$. If you need any specific operation done with this, such as taking partial derivatives, finding critical points, or evaluating at certain values, please let me know!

Would you like me to perform a specific analysis or operation on this expression?

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Related questions:

1. How do you find the partial derivative of this function with respect to $x$?
2. How do you find the partial derivative of this function with respect to $y$?
3. What are the critical points of this function?
4. How do you evaluate the function $Z$ at specific values of $x$ and $y$?
5. How can you use this function in optimization problems?

Tip:

When working with multivariable functions, it's often useful to understand how the function behaves in different directions, which is where partial derivatives come in handy!