One way to prove such a statement is to set it up a "truth table". Since each of the two elements, x, y, and z, can be either True or False, there are cases. If x= y= x= False, then x'= y'= z'= True so x'y'z is True while x'yz, x'yz, and xyz' are false. True+ False+ False+ False= True. The left side is True in this case. On the right, x xor y' is "False xor True= True" and so the right side becomes "True xor False= True".
Do the same with the other 7 cases and see if you get both sides the same in each case.