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महाराष्ट्र राज्य शिक्षण मंडळएचएससी विज्ञान (सामान्य) इयत्ता ११ वी

If A = [122212221], Show that A2 – 4A is a scalar matrix

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प्रश्न

If A = `[(1, 2, 2),(2, 1, 2),(2, 2, 1)]`, Show that A2 – 4A is a scalar matrix 

बेरीज
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उत्तर

A2 = A · A = `[(1, 2, 2),(2, 1, 2),(2, 2, 1)] [(1, 2, 2),(2, 1, 2),(2, 2, 1)]`

= `[(1 + 4 + 4, 2 + 2 + 4, 2 + 4 + 2),(2 + 2 + 4, 4 + 1 + 4, 4 + 2 + 2),(2 + 4 + 2, 4 + 2 + 2, 4 + 4 + 1)]`

= `[(9, 8, 8),(8, 9, 8),(8, 8, 9)]`

∴ A2 – 4A = `[(9, 8, 8),(8, 9, 8),(8, 8, 9)] - 4[(1, 2, 2),(2, 1, 2),(2, 2, 1)]`

= `[(9, 8, 8),(8, 9, 8),(8, 8, 9)] -[(4, 8, 8),(8, 4, 8),(8, 8, 4)]`

= `[(5, 0, 0),(0, 5, 0),(0, 0, 5)]`

which is a scalar matrix.

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पाठ 4: Determinants and Matrices - Exercise 4.6 [पृष्ठ ९५]

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