If the inner angles a, B and C of △ ABC are opposite to the sides a, B and C, and if the angles a, B and C form an arithmetic sequence in turn, and (a + C) 2 = 12 + B2, then the area of △ ABC is () A. 6-33B. 63-9C. 23D. 3

The angle a, B and C are in the sequence of arithmetic numbers. If ∵ 2B = a + C, a + B + C = 180 ° and ∵ B = 60 °, then B2 = A2 + c2-2accos 60 °, that is, B2 = A2 + c2-ac (1), and (a + C) 2 = 12 + B2 (2), then AC = 4 and ∵ s △ ABC = 12acsin 60 ° = 3 can be obtained by subtracting the two formulas

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