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设x,y满足约束条件,则z=x+y的最小值是
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高三下学期数学《》真题及答案
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设xy满足约束条件则z=2x-3y的最小值是
-7
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设变量xy满足约束条件则目标函数z=x+2y的最小值为A.2B.3C.4D.5
设变量xy满足约束条件则目标函数z=3x-2y的最小值为
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设xy满足约束条件则z=2x+y的最小值是.
设xy满足约束条件求目标函数z=2x-3y的最小值是
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设变量xy满足约束条件则目标函数z=3x-2y的最小值为
-5
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设变量xy满足约束条件则z=x-3y的最小值为
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设实数x和y满足约束条件则z=2x+3y的最小值为
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设变量xy满足约束条件则目标函数z=2x+y的最小值为
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设xy满足约束条件则目标函数z=2x﹣3y的最小值是___________
设变量xy满足约束条件则z=x-3y的最小值为________.
设xy满足约束条件则z=2x+3y–5的最小值为
设变最xy满足约束条件则目标函数z=x+2y﹣l的最小值为
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满足约束条件|x|+2|y|≤2的目标函数z=y-x的最小值是________.
设xy满足约束条件则z=2x﹣3y的最小值是
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设变量xy满足约束条件则目标函数z=x+2y的最小值为
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设变量xy满足约束条件则目标函数z=y-2x的最小值为
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设变量xy满足约束条件则目标函数z=2x+5y的最小值为
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设变量xy满足约束条件则目标函数z=3x-4y的最大值与最小值的和为_______.
设xy满足约束条件则目标函数z=-x+2y的最小值是.
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实验室常用的电流表和电压表都由电流计G其实就是小量程的电流表改装而成的.电流计G也是有电阻的同样遵从欧姆定律.现有一个满偏电流量程为3.0mA内阻为Rg=1Ω的电流计G.小明同学利用所学的物理知识将该电流计G改装成了一个既可以测量电流也可以测量电压的多用电表其电路原理如图所示.当接AB两个接线柱时可以当作量程是0.6A的电流表使用当接AC两个接线柱时可以当作量程为3V的电压表使用求电阻R1R2的阻值大小结果保留三位小数.
如图所示一台直流发电机D放在实验桌上质量为2kg的砝码用细绳直接绕在发电机的转轴上当砝码缓慢下降时发电机两端相连的灯泡会发光.砝码下降的高度为1.5m下降时所用的时间为3s小灯泡在发光这段时间发电机两端连接的电压表的读数为6V与灯泡串联的电流表的读数为1A.整个装置绳重摩擦不计发电机外部连接导线电阻忽略不计求 1砝码的重力在3s内所做功的功率. 2发电机的效率. 3发电机线圈的电阻r.
小明家电能表上月底的示数和本月底的示数如图所示他家本月消耗的电能为kW•h他家同时使用的用电器总功率不得超过W.
Asafirstresponderyouneverknowwhattypeofsituationyoumightwalkintoorwhoyou'llmeetalongtheway.That'sdefinitelybeenthecaseforJeffreyLanenberga51﹣year﹣oldparamedic急救医务人员since1984. TenyearsintothejobLanenbergreceivedacallthatreportedthatamaninhisearly30shadfallendownintheMallofAmerica.WhenLanenbergandhispartnerarrivedatthescenetheyfoundtheyoungmalefacedownontheground.Hehadgoneunconsciousmakingweakattemptstobreathe.Hiswifestoodbesidehimholdingtheirsmallsoninhorror.Theyquicklyrushedtodefibrillate除颤andcalmthemantokeephimundercontrol.AfterLanenbergdroppedthepatientoffattheneighboringhospitalhethoughtaboutthemanandhisfamilyforalongtime. LanenbergthoughthehadexperiencedeverythingunderthesununtilonerandomvisittoOfficeMaxthreeyearsagowherehemetamanrepeatedlywalkbackandforthwhilestaringathim.Asitturnedoutthemanwasthepatienthehadsaved20yearsearlier. Yougaveme20yearsmorethanIeverthoughtI'dhavethemansaid.HethankedLanenbergrepeatedlyandtoldhimhehadsomeonehewantedhimtomeet.Hesteppedaroundthecornerandreappearedwitha20﹣something﹣year﹣oldman.Lanenberginstantlyknewthatitwasthesonhehadseenstandingbyhismotherallthoseyearsago. ThatdaychangedmylifeLanenbergsaid.Beforethateverythingwasaboutwork…WhenItalktomybeginner﹣trainingclassItellthemyouneverknowtheimpactyoucanhaveonsomeone'slife. 1WhatdidLanenbergdowiththeyoungman? A.Hegavethemanthefirstaid. B.Hecuredthemanatthescene. C.Heonlysentthemantohospital. D.Hetookcareoftheman'swifeandson. 2WhatdidLanenbergthinkoftheencounterwiththeman? A.Itwasunbelievable. B.Itwasacommonroutine. C.Itwasamatterofcourse. D.Itwasadangeroussituation. 3WhywasthemanthankfultoLanenberg? A.Lanenberghelpedbringuphislittleson. B.Lanenbergdonatedtosupporthisfamily. C.Lanenberggavehimthepresenthappylife. D.Lanenbergtaughthissontobeanewdoctor. 4HowdidthemeetingchangeLanenberg'slife? A.Hechangedhisattitudetohisjob. B.Hewasrewardedwithmuchmoney. C.Hegotapromotiontobeateamleader. D.Hetookupteachingworktotrainnewcomers.
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如图所示的电路中电源电压保持不变R2=20Ω闭合开关S移动滑动变阻器R2的滑片到中点c时电流表的示数为0.4A移动滑片P到最左端a时电流表的示数为0.3A求电源电压和R1的阻值.
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用如图所示装置测量动滑轮的机械效率实验时竖直向上的匀速拉动弹簧测力计使挂在动滑轮下面的钩码缓缓上升.实验数据如表 1第①次实验时使钩码匀速升高0.2m所用的时间为2s则作用在绳子自由端的拉力F的功率为0.12W 2第②次实验时测得该动滑轮的机械效率约为90.9%结果保留到0.1% 3提高动滑轮机械效率的办法除了增加所提升的物体钩码的重量还可以减轻动滑轮的重量.如图所示若两次提升同一物体第一次所用的动滑轮重为G1时此时动滑轮的机械效率为75%第二次所用的动滑轮重为G2时此时动滑轮的机械效率为90%则G1与G2之比为31不计绳重及摩擦.
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如图所示O是支点在B端挂一重物可以在A端沿不同的方向分别施加F1F2F3三个力均可使杠杆在水平位置保持平衡下列关于这三个力大小关系的表达式正确的是
小华探究凸透镜的成像规律. 1课间小华到室外利用太阳光来测量凸透镜的焦距她将该凸透镜正对着太阳光如图甲所示.此时纸上呈现一个并非最小的光斑时测得这个光斑到凸透镜的距离为L.此时再将这个凸透镜与纸之间距离稍微增大若光斑变大则凸透镜的焦距fL选填“>”“<”或“=”调整以后得到该透镜的焦距为10cm. 2当烛焰位于如图乙所示位置时移动光屏可在光屏上得到一个清晰的像此成像规律常用在选填“放大镜”“照相机”或“幻灯机”上保持凸透镜位置不变将点燃的蜡烛放在光具座上20cm刻线处要在光屏上重新得到烛焰清晰的像应将光屏向选填“左”或“右”移动. 3当烛焰再次位于如图乙所示位置时若将蜡烛稍远离凸透镜光屏上的像变模糊若不移动光屏要再次在光屏上得到清晰的像则可在蜡烛和凸透镜之间再放上一个焦距合适的选填“近视眼镜”或“远视眼镜”.
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面镜不是使光线透过而是使光反射回去的仪器光线遵循反射定律如图甲是凹面镜它将平行主轴的入射的光线会聚在焦点F上这是因为表面每个点的法线方向不同光线以不同的角度反射根据光路可逆性凹面镜不仅可以使平行光线汇聚于焦点还能使过焦点的光线反射成平行于主轴的光请根据以上叙述在图乙中画出H0的成像光路图.
青春期后男生的声音变得“低沉”了这里的“低”主要指的是
在物理学中物体由于被举高而具有的能叫做重力势能可用Ep表示重力势能Ep与物体的质量m与被举的高度h之间的定量关系可用Ep=mgh表示物体由于运动而具有的能叫动能可用Ek表示物体的动能与物体的质量m运动速度v的定量关系可用Ek=mv2表示.如图所示一个质量m为5kg的物体从斜长s为10m倾角θ为30°的光滑斜面顶端由静止自由滑行到斜面底部不计空气阻力请完成下列问题 1求该物体自斜面顶端由静止自由滑行到斜面底部的过程中重力对物体做功多少焦耳 2由于斜面光滑且不计空气阻力则乙物体从斜面顶端滑行到斜面底部的过程中其机械能守恒.求该物体从斜面顶端由静止自由滑行到斜面底端的瞬时速度大小为多少
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