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(1)0(2)见解析
(1)f(x)的定义域为(0,+∞),
令f′(x)=
![](https://img.yulucn.com/upload/6/91/69117356df23f2de781dd40756f13240_thumb.jpg)
﹣1=0,解得x=1,
当0<x<1时,f′(x)>0,所以f(x)在(0,1)上是增函数;
当x>1时,f′(x)<0,所以f(x)在(1,+∞)上是减函数;
故函数f(x)在x=1处取得最大值f(1)=0;
(2)①由(1)知,当x∈(0,+∞)时,有f(x)≤f(1)=0,即lnx≤x﹣1,
∵a
k ,b
k (k=1,2…,n)均为正数,从而有lna
k ≤a
k ﹣1,
得b
k lna
k ≤a
k b
k ﹣b
k (k=1,2…,n),
求和得
![](https://img.yulucn.com/upload/3/0b/30be8ce5a4e481a4503284765397a215_thumb.jpg)
≤a
1 b
1 +a
2 b
2 +…+a
n b
n ﹣(b
1 +b
2 +…+b
n )
∵a
1 b
1 +a
2 b
2 +…a
n b
n ≤b
1 +b
2 +…b
n ,
∴
![](https://img.yulucn.com/upload/3/0b/30be8ce5a4e481a4503284765397a215_thumb.jpg)
≤0,即ln
![](https://img.yulucn.com/upload/a/aa/aaa06f4550f73035bed6c311360b034e_thumb.jpg)
≤0,
∴
![](https://img.yulucn.com/upload/c/ba/cba11b9e8ba1fa478429b737cb0d3217_thumb.jpg)
…
![](https://img.yulucn.com/upload/6/d3/6d3a4f149a62d6f5d93d077689b81012_thumb.jpg)
≤1;
②先证
![](https://img.yulucn.com/upload/2/8e/28e227b9032373ab115b0b2968b0a1b1_thumb.jpg)
≤
![](https://img.yulucn.com/upload/e/d7/ed7eb2caf18999b874d002f1c8b46e1f_thumb.jpg)
…
![](https://img.yulucn.com/upload/8/51/85127847345396fe9dd18fe2daca00b4_thumb.jpg)
,
令a
k =
![](https://img.yulucn.com/upload/c/3d/c3d0ec18f253aff601f9137735f1b6b0_thumb.jpg)
(k=1,2…,n),则a
1 b
1 +a
2 b
2 +…+a
n b
n =1=b
1 +b
2 +…b
n ,
于是由①得
![](https://img.yulucn.com/upload/4/2f/42f0a523c6f6e66e8fe3bbcba6538808_thumb.jpg)
≤1,即
![](https://img.yulucn.com/upload/6/53/65346e3db905f1872b7e6d8e8e14480e_thumb.jpg)
≤n
b1+b2+…bn =n,
∴
![](https://img.yulucn.com/upload/b/bb/bbb2caa1362d9d86bf0933d457bd6f39_thumb.jpg)
≤
![](https://img.yulucn.com/upload/c/b9/cb97542ecae0e7fcec2408201d24079b_thumb.jpg)
…
![](https://img.yulucn.com/upload/e/7e/e7e193e765d987b9d056ba4d1c989466_thumb.jpg)
,
②再证
![](https://img.yulucn.com/upload/d/21/d216bffb01f911a8d92850974e6f637d_thumb.jpg)
…
![](https://img.yulucn.com/upload/8/84/88468a45eb199ac5240b9025b65940fa_thumb.jpg)
≤b
1 2 +b
2 2 +…+b
n 2 ,
记s=b
1 2 +b
2 2 +…+b
n 2 .令a
k =
![](https://img.yulucn.com/upload/3/13/3135ec2acd08b2505a5b5df558017a2c_thumb.jpg)
(k=1,2…,n),
则a
1 b
1 +a
2 b
2 +…+a
n b
n =
![](https://img.yulucn.com/upload/1/53/1536215c3ebc39d7ab9f69099bb13708_thumb.jpg)
(b
1 2 +b
2 2 +…+b
n 2 )=1=b
1 +b
2 +…b
n ,
于是由(1)得
![](https://img.yulucn.com/upload/5/52/55277fd1431323b76db7c02d9b3fed37_thumb.jpg)
≤1,
即
![](https://img.yulucn.com/upload/1/c8/1c88c741e809288e9c593ec1640730c8_thumb.jpg)
…
![](https://img.yulucn.com/upload/6/69/669e1786ae5d98fc0f440e151f77f2ca_thumb.jpg)
≤s
b1+b2+…bn =s,
∴
![](https://img.yulucn.com/upload/1/c8/1c88c741e809288e9c593ec1640730c8_thumb.jpg)
…
![](https://img.yulucn.com/upload/6/69/669e1786ae5d98fc0f440e151f77f2ca_thumb.jpg)
≤b
1 2 +b
2
1年前
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