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先把 x x 当作幂函数（把指数上的 x 看作常数）求一次导，得 x x x 1 = x x, 再把 x x 当作指数函数（把底数上的 x 看作常数）求一次导，得 x x ln x, 最后把两者相加，得 (x x) = x x + x x ln x
Influencer, 29, and wife, 66 ‘open’ their marriage and tell each other
