21
? ab c a 3 b 2 - bc + c 2 + b 3 c 2 - ca + a 2 + c 3 a 2 - ab + b 2 3(ab + bc + ca) a + b + c X a 3 (b + c) b 3 + c 3 2 X a 3 b 2 + c 2 a + b + c a 3 b 2 + c 2 a + b + c 2 a λ+1 b λ + c λ λ 0 X a 3 (b + c) b 3 + c 3 2 X a 3 b 2 + c 2 2 a 3 b 2 + c 2 a + b + c a 3 (b + c) b 3 + c 3 a + b + c a 3 (b + c) b 3 + c 3 = a 3 b 2 - bc + c 2 a 3 b 2 - 1 2 (b 2 + c 2 )+ c 2 = 2a 3 b 2 + c 2 X a 3 (b + c) b 3 + c 3 2 X a 3 b 2 + c 2

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2

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