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Express the following matrices as the sum of a symmetric and a skew symmetric matrix: [(6, –2, 2),(–2, 3, –1),(2, –1, 3)]

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Question

Express the following matrices as the sum of a symmetric and a skew symmetric matrix:

`[(6, -2, 2),(-2, 3, -1),(2, -1, 3)]`

Sum
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Solution

A = `[(6, -2, 2),(-2, 3, -1),(2, -1, 3)]`

⇒ A = `[(6, -2, 2),(-2, 3, -1),(2, -1, 3)]`

∴ A + A' = `[(6,-2,2),(-2,3,-1),(2,-1,3)] + [(6,-2,2),(-2,3,-1),(2,-1,3)]`

= `[(6 + 6, -2 - 2, 2 + 2),(-1 - 1, 3 + 3, -1 - 1),(2 + 2, -1 - 1, 3 + 3)]`

= `[(12, -4, 4),(-4, 6, -2),(4, -2, 6)]`

∴ `1/2 (A + A') = 1/2 [(12, -4, 4),(-4, 6, -2),(4, -2, 6)]`

= `[(6, -2, 2),(-2, 3, -1),(4, -1, 3)]` is a symmetric matrix.

∴ (A – A) = `[(6, -2, 2),(-2, 3, -1),(4, -1, 3)] - [(6, -2, 2),(-2, 3, -1),(4, -1, 3)]`

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

∴ `1/2 (A - A') + 1/2 [(0, 0, 0),(0, 0, 0),(0, 0, 0)] = 0`

Hence, `A = 1/2 (A + A') + 1/2 (A - A')`

= `[(6, -2, 2),(-2, 3, -1),(2, -1, 3)] + [(0, 0, 0),(0, 0, 0),(0, 0, 0)]`

= `[(6, -2, 2),(-2, 3, -1),(2, -1, 3)]` = A

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Chapter 3: Matrices - EXERCISE 3.3 [Page 67]

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NCERT Mathematics Part 1 and 2 [English] Class 12
Chapter 3 Matrices
EXERCISE 3.3 | Q 10. (ii) | Page 67

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