[Math] NOT ((NOT A AND NOT B) OR (A AND NOT B)) simplification using de morgans law

boolean-algebra

I had my AS mock exam today, and this question came up. I've checked it on calculators and it says it simplifies to B, which is what I got in the exam, but I'm not entirely sure how I got there.

My understanding is that if you want to change the sign (in this case, the or), then you negate the terms on both sides, and then negate the overbar. You then simplify and solve.

I've sat here trying to solve it for ages, and I keep getting different results. I've written out the truth table and it matches, but I don't see how you simplify it
NOT((NOT A AND NOT B) OR (A AND NOT B))
From what I can see, I negate the terms in the two brackets, then negate the not at the beginning, and change the sign in the middle.
So what I have is (A AND B) AND (NOT A AND B)

A.NOTA.B.B

A.NOTA=0 right?

then B.B=B
so its B(0)=0, which isn't the answer.

I'm not sure how to apply the rule.

Best Answer

$$\begin{align} \overline{(\overline{A}\cdot\overline{B})+(A\cdot\overline{B})} &=\overline{\overline{A}\cdot\overline{B}}\cdot\overline{A\cdot\overline{B}}\tag{De Morgan's}\\ &=(A+B)\cdot(\overline{A}+B)\tag{De Morgan's}\\ &=A\cdot\overline{A}+A\cdot B+B\cdot\overline{A}+B\cdot B\tag{Expanding}\\ &=0+A\cdot B+B\cdot\overline{A}+B\\ &=B+A\cdot B+B\cdot\overline{A}\tag{Commutative}\\ &=B\cdot(1+A+\overline{A})\tag{Factorise}\\ &=B\cdot1\\ &=B\\ \end{align}$$

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