\vec{ AB } \;. \;\vec{ AC } \;= \; AB \; \times \; AC \; \times \; cos\, \widehat{BAC}

A = (8.1, -1.22)
B = (9.818919583606899, -5.980763246535767)
u = Vector(A, B)
a = Distance(A, B)
TexteAB: Name[A] + (Name[B]) + " \, = \, " + a
D = OrthogonalLine(A, u)
C = Point(D)
v = Vector(A, C)
α = Angle(u, v)
b = Distance(A, C)
TexteAC: Name[A] + (Name[C]) + " \, = \, " + b
texte2: "\vec{ AB } \;. \;\vec{ AC } \;= \;" + a + "\; \times \;" + b + "\; \times \; cos \;" + α + "\; = \;" + (a * b * cos(α))