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If A = [31-12], prove that A2 – 5A + 7I = 0, where I is unit matrix of order 2

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प्रश्न

If A = `[(3, 1),(-1, 2)]`, prove that A2 – 5A + 7I = 0, where I is unit matrix of order 2

If A = `[(3, 1),(-1, 2)]`, prove that A2 – 5A + 7I = 0, where I is 2 × 2 unit matrix and 0 is zero matrix of order 2.

योग
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उत्तर

Given: A = `[(3, 1),(-1, 2)]`

A2 = A · A

= `[(3, 1),(-1, 2)] [(3, 1),(-1, 2)]`

= `[(9 - 1, 3 + 2),(-3 - 2, -1 + 4)]`

A2 = `[(8, 5),(-5, 3)]`

Now consider

L.H.S. = A2 – 5A + 7I

= A . A – 5A + 7I

= `[(8, 5),(-5, 3)] -5[(3, 1),(-1, 2)] + 7[(1, 0),(0, 1)]`

= `[(8, 5),(-5, 3)] - [(15, 5),(-5, 10)] + [(7, 0),(0, 7)]`

= `[(8 - 15 + 7, 5 - 5 + 0),(-5 + 5 + 0, 3 - 10 + 7)]`

= `[(-7,0),(0,-7)] + [(7,0),(0,7)]`

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

= 0 = R.H.S.

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

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बालभारती Mathematics and Statistics (Arts and Science) Part 1 [English] Standard 11 Maharashtra State Board
अध्याय 4 Determinants and Matrices
Exercise 4.6 | Q 15 | पृष्ठ ९५

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