how to find cosinus betwen two vector? i have task in linear-algebra.
Condition:
we have triangle angles
A(-4,2);
B(-1,6);
C(8,-3);

How to find cosinus between BA and BC vectors?
please help :( what is solution for this task?

The dot product gets you just what you want.  The dot product of two vectors $\vec u \cdot \vec v = |\vec u||\vec v|\cos \theta$ where $\theta$ is the angle between the vectors.  So  $\cos \theta =\frac{\vec u \cdot \vec v}{|\vec u||\vec v|}$.  The dot product is calculated by summing the products of the components $\vec {BA} \cdot \vec {BC} = -4 \cdot -1 + 2 \cdot 6=4+12=16$
