$A'$, $B'$, $C'$, $D'$ are the centre off mass points in each triangle in a tetrahedron $ABCD$. What are the coordinates for the vectors $AB'$, $AC'$, $AD'$, $A'B'$ using $AB$, $AC$, $AD$.
So far:
$$k_1AB + k_2AC+k_3AD=AB'$$ I don't know how to continue