didn't realize bc let you define functions, that's awesome!

bcpp.sh should use a bash shebang, it does not run under a POSIX shell like dash.

algebra.bc's solve does produce wrong results on my machine, unsure how you're getting correct solutions with the linear term's sign flipped-- flipping it back to match the quadratic formula as you suggest in the comment produces correct results.

huh???? for me the function is flipped, so when it's like it currently is it works

bcpp.sh should use a bash shebang, it does not run under a POSIX shell like dash.
uhh idk what that means sorry
i'm planning to write it in something else anyways, i'm not a big fan of bash

$ bc --version
bc 1.07.1
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 Free Software Foundation, Inc.

I'm using bc 1.07.1 on Debian, and have been using solve(1, 5, 6) to test (which should produce x = -2.00000000000000000000 ∨ x = -3.00000000000000000000)

What version of bc are you using, and what coefficients are you using to test?

[~] > bc --version
bc 1.08.2
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2018, 2024 Free Software Foundation, Inc.

solve(1, 5, 6)
x = 3.00000000000000000000 ∨ x = 2.00000000000000000000

the above output is incorrect, the roots are negative: -3 and -2.

just installed bc 1.08.2 (running under mingw :P) and got the same results as i had before.