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(1 - x_1)(1 - x_2)(1 - x_3) >= 1/2 if x_1+x_2+x_3<=1/2 (2017 Auckland MO S2)

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November 15, 2021
algebrainequalities

Problem Statement

The sum of the three nonnegative real numbers x1,x2,x3 x_1, x_2, x_3 is not greater than 12\frac12. Prove that (1x1)(1x2)(1x3)12(1 - x_1)(1 - x_2)(1 - x_3) \ge \frac12