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某考试的一道超纲破题

作者:星野みや发布时间:2024-09-05

问题

这是2025届广东省高三毕业班调研考试(一)数学试卷的19题,这里省略掉无用的内容,而且给的材料也有问题:

  1. f(x)%3D%5Cdisplaystyle%5Cint%5Cleft(%5Cmathrm%20e%5Ex%2B1%5Cright)%5Cmathrm%20dx and f(0)%3D2.

    Find f(x).

  2. Find the area between the curves y%3Dx%5E2%2Cy%3D-x%2B6.

  3. f(x)%3D%5Cmathrm%20e%5Ex-1-2mx for all 0%5Cle%20b%3Ca such that %5Cdisplaystyle%5Cint_%7B0%7D%5E%7Ba%7Df(x)%5Cmathrm%20dx%3E%5Cint_%7B0%7D%5E%7Bb%7Df(x)%5Cmathrm%20dx.

    Find the range of m.

解答

这就是大学微积分的题,前面两问很简单,直接代入公式就可以了。

第1问解答:

%5Cbegin%7Balign%7D%0Af(x)%20%26%20%3D%20%5Cmathrm%20e%5Ex%2Bx%2BC%5C%5C%0Af(0)%20%26%20%3D%201%2BC%20%3D%202%5CRightarrow%20C%20%3D%201%5C%5C%0Af(x)%20%26%20%3D%20e%5Ex%2Bx%2B1%0A%5Cend%7Balign%7D

第2问解答:

%5Cbegin%7Balign%7D%0A%5Cbegin%7Bcases%7D%0Ay%20%3D%20x%5E2%20%5C%5C%0Ay%20%3D%20-x%2B6%0A%5Cend%7Bcases%7D%0A%5CRightarrow%0Ax%20%26%20%3D%20-3%2C2%5C%5C%0AS%26%3D%5Cint_%7B-3%7D%5E%7B2%7D%5Cleft%20%7C%20x%5E2%2Bx-6%20%5Cright%20%7C%20%5Cmathrm%20dx%5C%5C%0A%26%3D%5Cint_%7B-3%7D%5E%7B2%7D%5Cleft%20(%20-x%5E2-x%2B6%20%5Cright%20)%20%5Cmathrm%20dx%5C%5C%0A%26%3D%5Cleft%20%5B-%5Cfrac%7Bx%5E3%7D%7B3%7D-%5Cfrac%7Bx%5E2%7D%7B2%7D%20%2B6x%20%5Cright%20%5D_%7B-3%7D%5E%7B2%7D%5C%5C%0A%26%3D%5Cfrac%7B125%7D%7B6%7D%0A%5Cend%7Balign%7D

两曲线的图像

第3问其实用不到积分公式,只要用变上限积分,再根据其求导公式就可以把给出的条件写成函数单调性的定义,最终还是要求导判断的,这样就又回去了。

Let F(x)%3D%5Cdisplaystyle%5Cint_%7B0%7D%5E%7Bx%7Df(x)%5Cmathrm%20dx%2C%20f(x)%3DF'(x).

If %5Cforall0%3Ca%3Cb%2CF(a)%3EF(b), F(x) is decreasing for x%5Cge0.

Then f(x)%3D%5Cmathrm%20e%5Ex-1-2mx%3C0 for x%5Cge%200.

And we know f(0)%3D0. f(x) is decreasing for x%5Cge%200.

Then %5Cdisplaystyle%20f'(x)%3D%5Cmathrm%20e%5Ex-2m%3C0%5CRightarrow%20%20m%3E%5Cmin_%7Bx%5Cge0%7D%5Cfrac%7B%5Cmathrm%7Be%7D%20%5Ex%7D%7B2%7D%20%5CRightarrow%20m%3E%5Cfrac%7B1%7D%7B2%7D.

总结

一道破题,拿了大学的东西,其实很简单。高考绝对不可能这样考的,也完全不符合19题的难度。以前的教材是有定积分的内容的,不过现在的考纲上已经没有了,所以没有任何做的价值。总之很烂,没活硬整。


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