1.

If A is a square matrix such that A2 = A, then write the value of 7A – (I + A)3, where I is an identity matrix.

Answer»

7A – (I + A)3 = 7A - {I3 + 3I2A + 3I.A2 + A3

= 7A – {I + 3A + 3A + A2A} [ I3 = I2 = I, A2 = A] 

= 7A – {I + 6A + A2

= 7A – {I + 6A + A} = 7A – {I + 7A} 

= 7A – I – 7A = –I



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