There are already quite a few Mathematical functions built in the standard Mendix Equation Editor. The full list can be found here:
This list contains a number of useful functions like floor, absolute value, and powers. However this list is by no means exhaustive. If you want to go beyond this, there is not currently a math module in the app store. You may have to implement your logic using a Java Action. This will allow you to pass in your required input parameters and take full advantage of the Java Math libraries. These will be more complete than the Mendix equation editor could ever be.
If you can’t do what you want with the Mendix options, look into making a Java action.
You probably refer to this Mx8 module: https://appstore.home.mendix.com/link/app/112522/Mendix/Math-Module ?
You might try to port the code back to Mx7. You could try to just copy paste the code and see where it might go wrong.