If A = {xC : x2 = 1} and B = {xC : x4 = 1}, then write A B and B A.

Here,={XϵC:X2=1}


={1 ,-1}


B={xϵC:X4=1}


={1,-1,i,-i}


Now, AB=A(AB)


={1,-1}{1,-1}


=ϕ


And BA=B(AB)


={1,-1,i,-i}{1,-1}


={i,-i}


1