1.

If A is a square matrix such that A2 = I, then (A – I)3 + (A + I)3 – 7A is equal to : A. A B. I – A C. I + A D. 3A

Answer»

(A). A

Expansion of the given expression,

A3 – I3 + 3AI2 – 3A2I + A3 + I3 + 3AI2 + 3A2I – 7A 

2A3 – 7A + 6AI

2A2A – 7A + 6A 

2AI – A {A2 = I} 

2A – A

A

Option (A) is the answer.



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