[dba-Tech] Free "Mathematica" type software

I am brushing up on my mostly forgotten math, and seeking an app that can a)
format math formulae correctly, and b) accept arguments and then solve the
formulae. Anyone know of something that can do this? Now that I have
officially retired, price or lack thereof is paramount, since it's only a
hobby with me.

Apparently research shows that the most effective way to stave off
Alzheimer's is by constantly exercising the brain, to which end my
retirement has led to many free hours that were previously spent writing
software for clients. Now I'm learning Mandarin and Cantonese and reading
stuff about molecular biology -- oh, and playing a few games of chess a day.
I want to refresh my cobwebbed math grey cells.

Arthur