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    • 已知函数f(x)=ln(x+1)+ax若存在x∈[1,2],使不等式f'(x)≥2x成立,求a范围

    等差数列{An}的前n项和为Sn,已知A(m-1)+A(m+1)-A(m)²=0
    S(2m-1)=38,（括号内的数位于下标）则m=（）
    设等比数列{An}的前n项和为Sn,若A1=1,S6=4*S3,则A4=（）
    设函数f(x)=3x^2+a/x^3(x∈(o,+∞))求正数a的取值范围,使对于任意x∈(0,+∞)都有f(x)>=20.
    已知函数f（x）＝（ax＋1）×a的（－x）次幂，a＞0且a≠1
    （1） 讨论f（x）的单调性，并求出极值x0
    （2）若（1）中的x0＝g（a）在（1，e〕上的最小值

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    相关建议   2011-02-14

    最后一体的题目看的不是特明白，不太清楚你写的啥

    温馨提示：内容为网友见解，仅供参考
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    第1个回答  2011-02-14
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    （1）f′（x）=1x+1+a由f′（0）=0，得a=-1，此时f′（x）=1x+1-1．当x∈（-1，0）时，f′（x）＞0，函数f（x）在区间（-1，0）上单调递增；当x∈（0，+∞）时，f′（x）＜0，函数f（x）在区间（0，+∞）上单调递减；∴函数f（x）在x=0处取得极大值，故a=-1．（...

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    已知函数f(x)=ln(x+1)-ax(a∈R).(Ⅰ)若a=1,求证:当x>0时,f(x)<0...
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    已知函数f(x)=ln(ax+1)+x²-ax(a>0) (1)若x=1\/2是函数f(x)的一个...
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    设函数f(x)=ln(x+1)(1)若x>0证明:f(x)>2xx+2.(2)若不等式12x2≤f(x2...
    则g′(x)＝1x+1?2(x+2)?2x(x+2)2＝x2(x+1)(x+2)2．∵x＞0，∴g′（x）＞0，∴g（x）在（0，+∞）上是增函数．故g（x）＞g（0）=0，即f(x)＞2xx+2．（2）原不等式等价于12x2?f(x2)≤m2?2bm?3．令h(x)＝12x2?f(x2)＝12x2?ln(1+x2)，则h′(...

    已知函数f(x)=xlnx+ax(a∈R)(I)当a=0,求f(x)的最小值;(II)若函数f(x...
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    已知函数fx=ln(x+1)+kx^2(k∈R) (1)若函数y=fx在x=1处取得极大值,求k...
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