we can say two formulas are equal if left side and write side have the same truth values in all the cases
SO lets see saying it is not equal
so take A=(aᐯb)'
B=a' ^ b'
so to Prove that we can assign A=True and B=False in some case it is enough to show two statements are not equal
So B=False means either a or b are False
So take those values of a and b and check if we are getting a= True value for A which we will not get so it is a valid statement