Yea... you didn't help one bit. Your reponse is as vague as the first. Either you believe everyone is at the same level as you or you're bad at explaining concepts and probably like the back and forth conversation. Anyway I will figure it out. Thanks for showing your ego it helped a lot.;)

Because of this condition (b >= 10 ** 9).
I don't like to speak with people from "doesn't make sense" point of view.
Take care

I understand what you said but there is no way to know every single thing in math so... yea.

Also could you explain why -c/b; works ?

or did you just look at the solutions ?

Study nathetatics!

what you have here doesn't make any sense ?? why does your work but what i wrote doesn't

#include

double quadratic(double a, double b, double c)
{
double discriminant = (b * b) - (4 * a * c);
double x = sqrt(discriminant);

double x2 = ((-b ) + (x))/2*a;

return std::abs(x2) < 1e-12;
}

The - '0' is redundant because the values are not used except for comparison the each other

Clever!

elegant one!

Maybe this could help you: https://en.wikipedia.org/wiki/Conjugate_(square_roots) or https://www.dummies.com/education/math/calculus/how-to-solve-limits-by-conjugate-multiplication/

Emm.. can you share the links of the introductions or papers? Even the name of theory will be helpful.

Yes... a small bit of math.

Is there any theory of this solution?

well done