Ошибка [Linker error] undefined reference to `Triangulation::distPoints(tagPOINT&, tagPOINT&)'

double Triangulation::squareTriang(POINT &t1, POINT &t2, POINT &t3)
{
double a,b,c;
double Y,S;
a=distPoints(t1,t2);
b=distPoints(t2,t3);
c=distPoints(t3,t1);
Y=acos((a*a+c*c-b*b)/(2*a*c));
S=0.5*a*c*sin(Y);
return S;      
}

class Triangulation
{
public:
    Triangulation(){;};
    Triangulation( SList &listPoints ){ lp = listPoints; };
 
    void triangulation(vector <Polygon_> &vn);
    static bool isInTriangle(POINT &point, POINT &t1, POINT &t2, POINT &t3 );
    void inputPoints();
    void output();
    double max(double &t1, double &t2);
    double min(double &t1, double &t2);
    double distPoints(POINT &t1, POINT &t2);
    double squareTriang(POINT &p1, POINT &p2, POINT &p3);
    bool inTriang(vector<Polygon_> &vn, POINT &p);
    static double vp( POINT &a, POINT &b, POINT &c)
    { return (a.x*b.y - a.x*c.y - b.x*a.y + b.x*c.y + c.x*a.y - c.x*b.y ); }
    static double scp( POINT &a, POINT &b, POINT &c )
    { return( (c.x - b.x)*(a.x - b.x) + (c.y - b.y)*(a.y - b.y) ); }
    void appendtoTail(T &t){ lp.appendtoTail(t); }
    void clear(){ lp.clear(); }
    int size(){ return lp.size; }
 
private:
    SList lp;
    int direction;
 
    void determineDirection();
};

double distPoints(POINT &t1, POINT &t2)
{
if ((t1.x==t2.x)&&(t1.y==t2.y)) return 0;
double x1, x2, y1, y2;
x1=t1.x;
x2=t2.x;
y1=t1.y;
y2=t2.y;
Distance =sqrt(pow(x2-x1,2)+pow(y2-y1,2)); 
return Distance;  
}