$(A,B)$ and $(C,D)$ are parallel vectors, in the book I'm reading, it illustrates one case for this proposition: $(A,B)\sim (C,D) \implies (A,C)\sim (B,D)$ with the following figure:
And then there's an exercise asking me to draw that proposition in the case that $A,B,C,D$ are collinear. I'm not sure about the answer but I guess that to achieve that, I should think of null vectors. The only possibility I see to achieve collinearity between all them is to think of $A=B=C=D$. Is this the answer?
Edit: I guess this is a viable answer:
The vector $(A,B)$ approach to $(C,D)$ until one is over the other.