问题
选择题
设函数f(x)=xsinx ， x∈[ -
|
答案
由题意可得：f（x）=f（|x|），
因为当x∈[ 0 ，
]时，f′（|x|）=sinx+xcosx＞0，π 2
所以此时f（|x|）为增函数．
又由f（x1）＞f（x2），得f（|x1|）＞f（|x2|），
故|x1|＞|x2||，
所以x12＞x22．
故选B．
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设函数f(x)=xsinx ， x∈[ -
|
由题意可得：f（x）=f（|x|），
因为当x∈[ 0 ，
]时，f′（|x|）=sinx+xcosx＞0，π 2
所以此时f（|x|）为增函数．
又由f（x1）＞f（x2），得f（|x1|）＞f（|x2|），
故|x1|＞|x2||，
所以x12＞x22．
故选B．
| 完形填空。 | ||||
| Having lived in the house for so long, we found our kitchen looked old. We decided it was time to 1 the kitchen, and my husband and I were discussing 2 colors. The children, sitting nearby, suddenly all spoke together: "Not the measuring stick." "No," I 3 them. "Not the measuring stick." The measuring stick isn't a (an) 4 stick but the kitchen side of the door between our kitchen and dining room. Along the edge we've 5 each child's growth by making a mark showing his or her 6 on every birthday. Over the years so many colored pens, pencils and markers have been used, that now, this white door is somewhat like an abstract painting. Names and dates show different 7 , and I can tell by the script(手迹) who measured whom. An eight-year-old measured her three-year-old sister, a grandchild measured her grandmother, my husband measured me. At the parties, when this door 8 back and forth frequently, friends stop to 9 the names and dates. When we ask if they would like to be always remembered, they usually smile 10 and go back right up into place, 11 to be measured. Many of those listed on the door are still 12 ; some have stopped. Some remain with us only in 13 . When my mother came to see my eldest daughter graduate from university, we measured her too. It was her last visit to our home. We haven't 14 the new kitchen color plan yet, but one thing is certain: whatever color we choose, the back of the kitchen door will always remain 15 , with lots of names and dates in various colors. | ||||
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