# Do you Know Matrices ?

**Algebra**Level pending

\(\displaystyle A\) is the \(\displaystyle n \times n\) matrix whose elements are all \(\displaystyle '1'\) and\(\displaystyle B\) is the \(\displaystyle n \times n\) matrix whose diagonal elements are all \(\displaystyle 'n'\) and other elements are \(\displaystyle 'n-r'\) . Then \(\displaystyle A^{2}\) is a scalar multiple of A and hence , \(\displaystyle ( B-rI)[B - (n^{2}-nr+R)I]\) is ? Here \(\displaystyle I\) is the Identity matrix.