Implementation of Polygon class - c++

Question

I am writing a program that contains three classes: They are point, line and polygon. I have written the first two, but I am having trouble with the last one.
This class has to have two constructors, one of them builds an object with a point (tip of polygon) and another one builds it with a line. These functions have to be as follows:
polygon(point** arr,int size) and polygon(line** arr,int size).
I don't know why point and line are pointer to pointer? What are the attributes of the polygon class and how can I write polygon's constructor?
class point
{
private:
int first;
int second;
public:
point(void);
point (int x,int y);
point (const point& other);
int getX();
int getY();
int distance(point* other);//distance of two point
line* Line(point*);//build a line with two point
polygon* triangle(point*,point*);//build a triangle with three point
~point(void);
};
point::point(void)
{
first=0;
second=0;
}
point::point (int x,int y)
{
first=x;
second=y;
}
point::point(const point& other)
{
first=other.first;
second=other.second;
}
int point::gha(int a)
{
if(a>=0)
return a;
else
return -a;
}
int point::pow(int a)
{
return a*a;
}
int point::getX(){return first;}
int point::getY(){return second;}
int point::distance(point* other)
{
int d= sqrt((pow(first-other->first))+(pow(second-other->second)));
return d;
}
line* point::Line(point* other)
{
line l(this,other);
return &l;
}
polygon* point::triangle(point*,point*){
}
point::~point(void)
{
}
////////////////////////////
class line
{
private:
int m;
int c;
public:
line(void);
line(point*,point*);
line(int ,point*);
bool isParallel(line*);
bool isPrependicular(line*);
point* intersection(line*);
line* parallel(point*);
polygon* triangle(line*,line*);
~line(void);
};
line::line(void)
{
m=1;
c=0;
}
line::line(point* a,point* b)
{
m=((a->getY())-b->getY())/(a->getX()-b->getX());
c=a->getY()-(m*(a->getX()));
}
line::line(int dip,point* a)
{
m=dip;
c=a->getY()-(dip*(a->getX()));
}
bool line:: isParallel(line* other)
{
if(m==other->m)
return true;
else
return false;
}
bool line::isPrependicular(line* other)
{
if((m*other->m)==1 || (m*other->m)==-1)
return true;
else
return false;
}
point* line::intersection(line* other)
{
int x=(other->c-c)/(m-other->m);
int y=(m*x)+c;
point p (x,y);
return &p;
}
line* line::parallel(point* other)
{
line l(m,other);
return &l;
}
line::~line(void)
{
}
///////////////////////////////////
class polygon
{
private:
int count;
point* tip;
line* l;
public:
polygon(void);
polygon(point** arr,int size);
polygon(line** arr,int size);
bool isTriangle();
bool isSquare();
~polygon(void);
};