11 int solve_deg2(
double a, 
double b, 
double c, 
double& x1, 
double& x2);
    14     double a, 
double b, 
double c, 
double d, 
double& x0, 
double& x1, 
double& x2);
    17     double a, 
double b, 
double c, 
double d, 
double e, 
double& x0, 
double& x1,
    18     double& x2, 
double& x3);
 int solve_deg4(double a, double b, double c, double d, double e, double &x0, double &x1, double &x2, double &x3)
Reference : Eric W. 
 
int solve_deg2(double a, double b, double c, double &x1, double &x2)
 
int solve_deg3(double a, double b, double c, double d, double &x0, double &x1, double &x2)
Reference : Eric W.