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

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प्रश्न

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

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

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बालभारती Mathematics and Statistics 1 (Arts and Science) [English] Standard 11 Maharashtra State Board
अध्याय 4 Determinants and Matrices
Exercise 4.6 | Q 12 | पृष्ठ ९५

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