In dimension $2$, we have the identity
$$\det(A+B) + \mbox{tr}(AB) = \det(A) + \det(B) + \mbox{tr}(A) \mbox{tr}(B)$$
but this is false when the dimension is $3$ or higher. So, we need that when dimension is $3$:
$$\det(A+B+C)=?$$
In dimension $2$, we have the identity
$$\det(A+B) + \mbox{tr}(AB) = \det(A) + \det(B) + \mbox{tr}(A) \mbox{tr}(B)$$
but this is false when the dimension is $3$ or higher. So, we need that when dimension is $3$:
$$\det(A+B+C)=?$$