A = (-3, -2)
B = (4, 5)
a = 10 (slider from 1 to 10, step 1)
u = Vector(A, B)
b = 4 (slider from 1 to 5, step 1)
u_0 = UnitVector(u)
l = Length(u)
TP: A + ((a / (a + b) * l) * u_0)