江西省2024年初中学业水平考试冲刺(一)1数学.考卷答案

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江西省2024年初中学业水平考试冲刺(一)1数学.考卷答案试卷答案

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分析令f(x)=$\frac{1}{2}$x2-2lnx,利用导数法求出函数的最值,进而可得关于x的方程$\frac{1}{2}$x2-2lnx=m在区间[$\frac{1}{e}$,e]上有实数解时,m的范围.

解答解:令f(x)=$\frac{1}{2}$x2-2lnx,
则f′(x)=x-$\frac{2}{x}$=$\frac{{x}^{2}-2}{x}$,
当x∈[$\frac{1}{e}$,$\sqrt{2}$)时,f′(x)<0,f(x)为减函数,x∈[$\sqrt{2}$,e]时,f′(x)>0,f(x)为增函数,
故当x=$\sqrt{2}$时,f(x)取最小值1-ln2,
又由x=$\frac{1}{e}$时,f(x)=$\frac{1}{2{e}^{2}}+2$,x=2时,f(x)=$\frac{{e}^{2}}{2}-2$,
故x=$\frac{1}{e}$时,f(x)取最大值$\frac{1}{2{e}^{2}}+2$,
若x的方程$\frac{1}{2}$x2-2lnx=m在区间[$\frac{1}{e}$,e]上有实数解,
m∈[1-ln2,$\frac{1}{2{e}^{2}}+2$]

点评本题考查的知识点是函数的零点的判定定理,函数的值域,难度中档.