题目

求函数y=+的值域. 答案：解:函数的定义域x∈［1,+∞),∵()2-()2=3,    令=·,=·(0≤t＜1),    则函数可转化成y=·+·=--·.    再令X=t2,Y=t,则y=--·,其中X=Y2(0≤Y＜1).    设k=,则k表示定点A(1,-2)与抛物线Y2=X(0≤Y＜1)上的动点P(X,Y)连线的斜率(如图).k≤kOA,    而kOA==-2,∴k≤-2.    根据y=--k,可得y≥,    即所求函数的值域是［,+∞).评述:本A new planet more like Earth was discovered   and regarded as a likely future home for human. The planet contains both land   and water with average temperatures around 22℃. It is 600 light years from Earth. There are 290 days a year on the planet.A French company wants to change the Eiffel   Tower into a very tall and growing Christmas tree made of 600,000 plants. The   Eiffel Tower is decorated（装饰）with 10,000 light bulbs and attracts（吸引）7   million visitors a year.Wow, what a night! The evening got off to a   fun start with Steven Hall. Ronan Parke took on Kelly Clarkson’s Because   Of You. Jai McDowall finally won because of his wonderful performance.1.The new planet     A.might have 365 days a yearB.has no waterC.might be a future home for humanD.has bad weather2.   will make the Eiffel Tower become a big treeA.1000 light bulbsB.600,000 plantsC.600 light yearsD.7 million visitors3.    was the winner of Britain’s Got Talent 2011A.Steven HallB.Ronan ParkeC.Kelly ClarksonD.Jai McDowall