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Question
A + I = `[(3, -2),(4, 1)]` then find the value of (A + I)(A − I)
Solution
A + I = `[(3, -2),(4, 1)]`
∴ A − I = (A + I) − 2I
= `[(3, -2),(4, 1)] - [(2, 0),(0, 2)]`
= `[(1, -2),(4, -1)]`
∴ (A + I) (A – I) = `[(3, -2),(4, 1)] [(1, -2),(4, -1)]`
= `[(3 - 8, -6 + 2),(4 + 4, -8 - 1)]`
= `[(-5, -4),(8, -9)]`
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