I have a K-Map and I need to figure out which expression isn't equivalent to the provided K-Map.
$$\begin{array}{r|cccc}_{xy}\backslash^{wz}&00&01&11&10\\\hline00&0&\times&0&0\\01&0&\times&1&1\\11&1&1&1&1\\10&0&\times&0&0\end{array}$$
Which functions does not implement Karnaugh map above?
a) $(w+x)y$
b) $xy+yw$
c) $(w+x)(\overline w+y)(\overline x+y)$
d) none
We know that both options (a) and (b) are equivalent, and both represent the K-Map's function.
Option (c) however, turns to $(x)(x+w)$ if we make a subcube of size 8 using the first and last row, and a subcube of $00-01$ on both axes ($\text{size} = 4$).
If however we take the first row and last row as different subcubes, and the subcube of $00-01$, we get the function $= (x'+y)(x+y)(x+w)$.
Which of the above two methods gives the right answer (i.e., is the correct method)?
To complicate matters further, the answer key lists the answer to the question as (d) none, but I find the answer to be (c). Is the book's answer wrong? Or am I wrong?