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高中数学选择性必修 第二册(381题)


已知函数 \(f\left( x \right) = {x^2}\left( {x - 2} \right)\).


\(f\left ( {x} \right )\)在区间 \(\left[ { - 1,3} \right]\) 上的最大值和最小值.




知识点:第五章 一元函数的导数及其应用


参考答案:由(1)可知,函数\(f\left( x \right)\)在\(\left[ { - 1,0} \right)\)上单调递增,在\(\left( {0,\frac{4}{3}} \right)\)上单调递减,在\(\left( {\frac{4}{3},3} \right]\)上单调递增,所以,\(f{\left( x \right)_{极大值}} = f\left( 0 \right) = 0\), \(f{\left( x \right)_{极小值}} = f\left( {\frac{4}{3}} \right) = - \frac{{32}}{{27}}\),

又因为 \(f\left( { - 1} \right) = - 3\), \(f\left( 3 \right) = 9\) ,所以,

由(1)知 \(x = 0\) 是\(f\left ( {x} \right )\)的极大值点, \(x = \frac{4}{3}\) 是\(f\left( x \right)\)的极小值点,

所以 \(f\left( x \right)\)极大值\( = f\left( 0 \right) = 0\), \(f\left( x \right)\)极小值\( = f\left( {\frac{4}{3}} \right) = - \frac{{32}}{{27}}\) ,

又 \(f\left( { - 1} \right) = - 3\) , \(f\left( 3 \right) = 9\) , \(f{\left( x \right)_{\max }} = 9\) ,\(f{\left( x \right)_{\min }} = - 3\) .

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