B = (3, 4)
A = (1, 2)
AB = Vector(A, B)
a = 2 (slider from -5 to 5, step 0.1)
b = -3 (slider from -5 to 5, step 0.1)
k = 2 (slider from -5 to 5, step 0.1)
ABe2: AB * AB
FABi: k * a * b / ABe2
ABu = UnitVector(AB)
FBA: FABi * ABu
C = (5, 2)
c = 3 (slider from -5 to 5, step 0.1)
CB = Vector(C, B)
CBu = UnitVector(CB)
FBCi: k * b * c / (CB * CB)
FBC: FBCi * CBu
FB: FBA + FBC