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Let A = - 4 - 3 - 3 1 a 1 4 b 3 and A = A - 1 , then a + 2 b is equal to

Options

  1. A0
  2. B4
  3. C8
  4. D5

Correct answer

C. 8

Step-by-step solution

∴ A = A - 1 ⇒ A 2 = I A 2 = A ⋅ A = − 4 − 3 − 3 1 a 1 4 b 3 − 4 − 3 − 3 1 a 1 4 b 3 = 1 12 - 3 a - 3 b 0 a - 3 + a 2 + b a b - 4 - 12 + a b + 3 b b - 3 ∴ A 2 = I ⇒ a = 0 , b = 4 ⇒ a + 2 b = 8

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