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Question
Prove that A + AT is a symmetric and A – AT is a skew symmetric matrix, where A = `[(5, 2, -4),(3, -7, 2),(4, -5, -3)]`
Solution
A = `[(5, 2, -4),(3, -7, 2),(4, -5, -3)]`
∴ AT = `[(5, 3, 4),(2, -7, -5),(-4, 2, -3)]`
∴ A + AT = `[(5, 2, -4),(3, -7, 2),(4, -5, -3)] + [(5, 3, 4),(2, -7, -5),(-4, 2, -3)]`
= `[(5 + 5, 2 + 3, -4 + 4),(3 + 2, -7 - 7, 2 - 5),(4 - 4, -5 + 2, -3 - 3)]`
∴ A + AT = `[(10, 5, 0),(5, -14, -3),(0, -3, -6)]`
∴ (A + AT)T = A + AT i.e., A + AT = (A + AT)T
∴ A + AT = is a symmetric matrix.
A – AT = `[(5, 2, -4),(3, -7, 2),(4, -5, -3)] - [(5, 3, 4),(2, -7, -5),(-4, 2, -3)]`
= `[(5 - 5, 2 - 3, -4 - 4),(3 - 2, -7 + 7, 2 + 5),(4 + 4, -5 - 2, -3 + 3)]`
= `[(0, -1, -8),(1, 0, 7),(8, -7,0)]`
∴ (A – AT)T = `[(0, 1, 8),(-1, 0, -7),(-8, 7,0)]`
= `[(0, -1, -8),(1, 0, 7),(8, -7,0)]`
∴ (A – AT)T = – (A – AT)
i.e., A – AT = – (A – AT)T
∴ A – AT is a skew symmetric matrix.
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