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∛a = x, a = x³ ∛b = y b = y³ x + y = 2 x³ + y³ = 4 (x+y)3 - 3.x.y(x+y) = 4 23 - 3.xy(2) = 4 xy = 2/3 a.b = x³.y³ = 8/27