sqrt

[alexbg]

earetgwetserta

[alexbg]

deleted

[ne555]

Suppose v and u are vectors.
The dot product

uv = |u| |v| cos(theta)

where theta is the angle between the vectors.
So if the vectors are normalised then

uv = cos(theta)

[alexbg]

thanks, but how can i assign that the line between p1 and p2 is line v?

[ne555]

I don't know what is a your class Line. You don't need it.
Just use the points: a vector is the difference between two points.

Point p[3];
math::vector v[3]; 
for(int K=0; K<3; K++){
  v[K] = p[K] - p[ (K+1)%3 ]; //circular list
  v[K].normalize();
}
for(int K=0; K<3; K++)
  cout << v[K]*v[ (K+1)%3 ] << ' '; //show the cosines (again with circular list) 

PS: the class math::vector doesn't exists, but I think you get the idea