vec(AB) =(6,2) |AB| =sqrt(40)
vec(AC)=(3,-4) |AC| = 5
vec(AB)*vec(AC )= 10
cosA = 10 / |AB|* |AC| = 1/sqrt(10)
vec(AB) =(6,2) |AB| =sqrt(40)
vec(AC)=(3,-4) |AC| = 5
vec(AB)*vec(AC )= 10
cosA = 10 / |AB|* |AC| = 1/sqrt(10)