I am having a hard time with this problem (picture attached). I always have difficulty with proof-like problems such as this one. I guess I just don't really have the mathematical intuition needed for these types of problems.
I am not seeing how this identity works, because I thought my professor said that mew is equivalent to x bar, so I don't even understand how this identity makes sense. Can somebody help me with this problem?? I am supposed to verify the identity shown in the picture.