MCQ
If $A$ and $B$ are two matrices such that $AB = B$ and $BA = A,$ then ${A^2} + {B^2} = $
- A$2AB$
- B$2BA$
- ✓$A + B$
- D$AB$
Therefore ${A^2} + {B^2} = AA + BB = A(BA) + B(AB)$
$ = (AB)A + (BA)B = BA + AB = A + B$,
$(\because \,\,AB = B$ and $BA = A)$.
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