#include <math.h>
#include <stdio.h>

int main(void)
{
  float a, b, c; //input
  float x1, x2; //output
  float D;

  float eps = 1e-6;
  printf("Введите 3 числа через enter\n");
  scanf("%f %f %f", &a, &b, &c);
  if (fabsf(a) < eps)
  {
    printf("The data isn't correct!");
  }
  else {

    D = b * b - 4 * a * c;

    if (D < 0)
    {
      printf("The solution isn't correct!");
    }
    else {
      if (fabsf(D) < eps) //|D-6| < eps
      {
        x1 = -b / (2 * a);
        printf("x1: %f", x1);
      }
      else {
        x1 = (-b + sqrt(D)) / (2 * a);
        x2 = (-b - sqrt(D)) / (2 * a);

        //printf("(x1, x2): (%f, %f)", x1, x2);
        printf("x1 = %f\n", x1);
        printf("x2 = %f", x2);
      }
    }
  }

  printf("\n\n\n");
/*
Вывод
gcc -lm test.c && ./a.out
Введите 3 числа через enter
1
2
3
The solution isn't correct!
*/
  return(0);
}