设函数F(x,y)在(x0,y0)某邻域有连续的二阶偏导数,且F(x0,y0)=F’

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问题:

设函数F(x,y)在(x0,y0)某邻域有连续的二阶偏导数,且F(x0,y0)=F’x(x0y0)=0,F’y(x0,y0)>0,F"xx(x0,y0)<0.由方程F(x,y)=0在x0的某邻域确定的隐函数y=y(x),它有连续的二阶导数,且y(xn)=y0,则

A.y(x)以x=x0为极大值点.

B.y(x)以x=x0为极小值点.

C.y(x)在x=x0不取极值.

D.无法判断上述结论是否成立.

考点:普通考研考研数学(一)考研数学一
题型:单项选择题

After Mom died, l began visiting Dad every morning before I went to work. He was frail and moved slowly, but he always had a glass of freshly squeezed orange juice on the kitchen table for me, along with an unsigned note reading," Drink your juice." Such a gesture, l knew, was as far as Dad had ever been able to go in expressing his love. In fact, l remember, as a kid I had questioned Mom "Why doesn't Dad love me?" Mom frowned, "Who said he doesn’t love you?" "Well, he never tells me, "I complained." He never tells me either," she said, smiling. " But look how hard he works to take care of us, to buy us food and clothes, and to pay for this house. That's how your father tells us he loves us. "

I nodded slowly. I understood in my head, but not in my heart. l still wanted my father to put his arms around me and tell me he loved me. Dad owned and operated a small scrap (片) metal business, and after school I often hung around while he worked. Dad handled scrap steel into a device that chopped it as cleanly as a butcher chops a rack of ribs. The machine looked like a giant pair of scissors, with blades thicker than my father's body. If he didn’t feed those terrifying blades just right, he risked serious injury. "Why don' t you hire someone to do that for you?" Mom asked Dad one night as she bent over him and rubbed his aching shoulders with a strong smelling liniment. "Why don’t you hire a cook?" Dad asked, giving her one of his rare smiles.

Many years later, during my first daily visit, after drinking the juice my father had squeezed for me. l walked over, hugged him and said, "I love you, Dad." From then on I did this every morning. My father never told me how he felt about my hugs, and there was never any expression on his face when I gave them.

小题1:What would be the best title for the passage?

A.My father never loved me

B.I just couldn't understand my father

C.My hard-working father

D.Silent fatherly love小题2:The author’s father always prepared a glass of freshly squeezed orange juice for him because____.

A.that was the author's favorite

B.that was a gesture of love

C.the author was always complaining

D.he was sure the author would be thirsty小题3:The author’s father didn’t hire a helper because________.              .

A.he wanted to save money

B.his job required high skills

C.his job was too dangerous

D.he was not good at communicating with others小题4:We may infer from the passage that _______.

A.the author's father lacked a sense of humor

B.the author's-father didn't love him very much

C.the author quite understood his father as time went on

D.the author's father was too strict with him

题型:单项选择题

无土栽培存在的缺点?

题型:单项选择题

监理单位的义务包括______。
①选择承担工程项目建设的承建单位 ②与承建单位签订施工合同
③公正地维护有关各方的合法权益 ④不得泄露与本工程有关的保密资料
⑤不得参与可能与业主利益相冲突的承建单位组织的活动

A.①③⑤

B.①④⑤

C.②③④

D.③④⑤

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下列自然条件下()对金属的腐蚀不属于电化学腐蚀。

A、海水

B、地下水

C、潮湿大气

D、氧气

题型:单项选择题

安装滚筒时,就保证滚筒轴心线与机架长度在()。

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