How do the calculators solve the equations like ax³+bx²+cx+d=0? Is there any specific formula of it? If yes, what's the formula?

Answer 1

You could build on this idea
https://code.sololearn.com/c0MP4vcriFf5

Answer 2

I dont know what language calculators are written in (assembly or C I would guess), and I dont know the formula. But I think if you know how polynomials work and how they are solved, it wouldnt be too hard to write code that solves them.