求函数f(x)=x^3-3x^2-9x+1 的单调区间极值

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f'(x) = 3x² - 6x - 9 = 3(x + 1)(x - 3) = 0
x < -1: f'(x) > 0, 递增
-1 < x < 3: f'(x) < 0, 递减
x > 3: f'握卖激(x) > 0, 递段袜增
极大值: f(-1) = 6
极小值配早: f(3) = -26

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