sympy is not defined

It seems that you are trying to use the "sympy" module in Python but it is not defined. "sympy" is a third-party library for symbolic mathematics in Python and needs to be installed before it can be used. You can install it by running the following command in your terminal or command prompt:

pip install sympy

Once installed, you can import and use it in your Python code by adding the following line at the beginning:

import sympy