the answer is A+B
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given AB=A and BA=A
A^2+B^2=AA+BB
=BABA+ABAB
=BBA+AAB(since ab=b and ba=a)
=BA+AB(since ba=a and ab=b)
=A+B(since ba=a and ab=b)
A^2+B^2=AA+BB
=BABA+ABAB
=BBA+AAB(since ab=b and ba=a)
=BA+AB(since ba=a and ab=b)
=A+B(since ba=a and ab=b)