Is it necessary to have all variables of a boolean expression in its POS or SOP form?

Question

For example, if we have a boolean expression, anything like:

X= A′ B + CD + (A+B)′ [ACD + (BE)′ ]

We know this can be CD + A'. Can we just write the final POS or SOP using only A,C,D variables, omitting B and E? How to write SOP or POS form of such variables?

Answer 1

If B and E have absolutely no effect on X, then you don't need to use them in the equation.