can't use mathcad

If you download the free trial of Mathcad (currently Prime 7.0), you have thirty days of the full version of Mathcad.   After that, you have Prime Express.  Express will allow you to open and view files as they were filed; but by itself it is a powerful piece of software even with all of the "premium" features disabled.

FAQ about PTC education's licensing program: https://www.ptc.com/en/blogs/cad/free-downloads-for-students-part-2-ptc-academic-licensing-explained

Mathcad Prime 7.0:

https://www.mathcad.com/en/try-and-buy/mathcad-express-free-download/install

https://free-dl.ptc.com/install/pim_installmgr_mathcad.exe

Mathcad 15 M050:

https://www.ptc.com/-/media/Files/Docs/Mathcad/Mathcad15-EN.zip