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Question
If [aij]3×3 where aij = 2(i – j). Find A and AT. State whether A and AT are symmetric or skew-symmetric matrices?
Solution
A = [aij]3×3 = `[("a"_11, "a"_12, "a"_13),("a"_21, "a"_22, "a"_23),("a"_31, "a"_32, "a"_33)]`
Given that : aij = 2(i – j),
∴ a11 = 2(1 – 1) = 0,
a12 = 2(1 – 2) = –2,
a13 = 2(1 – 3)= –4,
a21 = 2(2 – 1) = 2,
a22 = 2(2 – 2) = 0,
a23 = 2(2 – 3) = – 2,
a31 = 2(3 – 1) = 4,
a32 = 2(3 – 2) = 2,
a33 = 2(3 – 3) = 0
∴ A = `[(0, -2, -4),(2, 0, -2),(4, 2, 0)]`
∴ AT = `[(0, 2, 4),(-2, 0, 2),(-4, -2, 0)]`
∴ AT = `-[(0, -2, -4),(2, 0, -2),(4, 2, 0)] = -"A"`
∴ AT = – A and A = – AT
∴ A and AT both are skew-symmetric matrices.
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