1.

How many different diagonal matrices of order n can be formed which are idempotent ?

Answer» Correct Answer - `2^(n)`
Matrix A is diagonal matrix.
`:. A`=dia. `(a_(1), a_(2), ..., a_(n))`
`implies A^(2)=` dia. `((a_(1))^(2), (a_(2))^(2),..,(a_(n))^(2))`
since A involuntary, we have
`:. A^(2)=A`
`implies (a_(1))^(2)=a_(1), (a_(2))^(2)=a_(2), ..., (a_(n))^(2)=a_(2),...,(a_(n))^(2)=a_(n)`.
`implies a_(1), a_(2), ..., a_(n)=0, 1`.
Thus, number of required matrix A is `2xx2xx2xx...n` times `=2^(n)`


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