《锐角三角函数复习》课堂教学实录

在高压缸排汽的总管上装有动力控制止回阀，以便在事故情况下切断，防止蒸汽返回到汽轮机，引起汽轮机超速。在高压缸排汽总管的端头有蒸汽冲洗接口，以供在管道安装完毕后进行冲洗，在管道冲洗完成后用堵头堵死。centerpinchecksandanchoringtheinnercylinder.AccordingtoWhilecouplingalignmentshouldkeepoiloutofcavityandlocatetherotoraxisneckraisedarewithintheprescribedlimits,thereshouldbenogaps,Horn,HornandHorn0.05mmfeelergaugesfitinto.Centercoupling,condenserwaterfillingandwater-filledaccordingtofactoryrequirement.ForcouplingthreesupportedrotorCenter,themouthunderthecouplingbetweenthevalueshouldbeasstipulatedinthemanufacturer,usually0.15~0.25mm.Inthecaseofcouplingconnection,ifpossible,liftingonlyonebearingendofthesupportbearingoftherotor,removethebearing,fittedwithspecialtilesandspecialliftingtools,discrotors,checkthejournalfluttertile,shouldgenerallybelessthan0.10MM.Whenthecouplingsandrotorcomeswhenthereisaconflict,thecouplingCentreshallprevail.6.4.5.2.2shaftlookingfor:...6.4.5.3.Provisionalboltconfirmedthepositioningoftherotorsize,aswellasthecouplingbetweentheadjustmentshimthicknessaccuracy,drawingstomeetthetechnicalrequirements.Plane,cylindricalandcleanthecouplingboltholesshouldbecleanandwithoutburrs,scrapironandgrease-free,relativepositionofthecouplingaccordingtothedrawingrequirementsare.Couplingtopscrews,rounddistanceapart,indicatorstomonitormovementoftheaircraft,itsvalueisallowedtopassthevalueaxismoving,mountedadjustmentpads,notepadsinstallationdirectionguidepincouplingwithprocessendclosed.Thebackwheelsslowlytightened,when2mmorso,withstandardwhitebarswheretwobackwheelboltholemeasurementaboveandbelow,confirmtwobackwheelboltholeconcentricity.Then,thesymmetricalhorizontalmounttwotemporaryboltstightened,attentiontomonitordialindicator,theninstallthesymmetricaltemporarybolts,thistimesitesslowlymovingrotor,inthemeasuredcircumferenceof8equalpartsbackwheelrimrock,eachmeasuringrelativechangesinvalueshouldbelessthan0.02mm.6.4.5.4couplingreamedandpairedboltreamingdiereamer,adjustablereamers,boringmill,inseveralways.6.4.5.4.1Generalrequirementsbeforereamingorboring,《锐角三角函数复习》课堂教学实录课题：人教版初中数学九年级下册《锐角三角形》（复习课）教学过程：一、基础知识之自我回顾师：昨天老师已经布置同学们课后自己对本章进行复习整理，现在展示你们成果的时候到了．生1：锐角三角函数的定义：直角三角形中，锐角的正弦值等于该角的对边与斜边的比值．直角三角形中，锐角的余弦值等于该角的邻边与斜边的比值．直角三角形中，锐角的正切值等于该角的对边与邻边的比值．生2：特殊角三角函数值要熟记．生3：解直角三角形及其应用时，对照图形，寻找已知量与未知量之间的关系．师：刚才几名同学的回答，汇总起来就是本章要掌握的知识，老师把它们总结成下面的网络图（投影）二、基础知识之基础演练（教者投影题目，学生思考后回答）1．计算1sin60cos302______生4：结果为14师：正确．2．在RtABC中，90C，若2ACBC，则tanA的值是（）A.12B.2C.55D.52生5：画出图形，容易求出1tan2A，所以选A．师：正确．3．在RtABC中，90,25CAB，15AC，则A的值是（）A.90B.60C.45D.30生6：由153cos225ACAAB，可得30A，故选D．师：正确．三、基础知识之灵活运用．（教者投影题目，学生思考后回答）1．ABC中，3,5,4abc，则sinA值是（）直角三角形中的边角关系锐角三角函数解直角三角形在高压缸排汽的总管上装有动力控制止回阀，以便在事故情况下切断，防止蒸汽返回到汽轮机，引起汽轮机超速。在高压缸排汽总管的端头有蒸汽冲洗接口，以供在管道安装完毕后进行冲洗，在管道冲洗完成后用堵头堵死。centerpinchecksandanchoringtheinnercylinder.AccordingtoWhilecouplingalignmentshouldkeepoiloutofcavityandlocatetherotoraxisneckraisedarewithintheprescribedlimits,thereshouldbenogaps,Horn,HornandHorn0.05mmfeelergaugesfitinto.Centercoupling,condenserwaterfillingandwater-filledaccordingtofactoryrequirement.ForcouplingthreesupportedrotorCenter,themouthunderthecouplingbetweenthevalueshouldbeasstipulatedinthemanufacturer,usually0.15~0.25mm.Inthecaseofcouplingconnection,ifpossible,liftingonlyonebearingendofthesupportbearingoftherotor,removethebearing,fittedwithspecialtilesandspecialliftingtools,discrotors,checkthejournalfluttertile,shouldgenerallybelessthan0.10MM.Whenthecouplingsandrotorcomeswhenthereisaconflict,thecouplingCentreshallprevail.6.4.5.2.2shaftlookingfor:...6.4.5.3.Provisionalboltconfirmedthepositioningoftherotorsize,aswellasthecouplingbetweentheadjustmentshimthicknessaccuracy,drawingstomeetthetechnicalrequirements.Plane,cylindricalandcleanthecouplingboltholesshouldbecleanandwithoutburrs,scrapironandgrease-free,relativepositionofthecouplingaccordingtothedrawingrequirementsare.Couplingtopscrews,rounddistanceapart,indicatorstomonitormovementoftheaircraft,itsvalueisallowedtopassthevalueaxismoving,mountedadjustmentpads,notepadsinstallationdirectionguidepincouplingwithprocessendclosed.Thebackwheelsslowlytightened,when2mmorso,withstandardwhitebarswheretwobackwheelboltholemeasurementaboveandbelow,confirmtwobackwheelboltholeconcentricity.Then,thesymmetricalhorizontalmounttwotemporaryboltstightened,attentiontomonitordialindicator,theninstallthesymmetricaltemporarybolts,thistimesitesslowlymovingrotor,inthemeasuredcircumferenceof8equalpartsbackwheelrimrock,eachmeasuringrelativechangesinvalueshouldbelessthan0.02mm.6.4.5.4couplingreamedandpairedboltreamingdiereamer,adjustablereamers,boringmill,inseveralways.6.4.5.4.1Generalrequirementsbeforereamingorboring,ACBA.34B.54C.35D.45生7：由3sin4aAc知选C师：有不同意见的吗？生8：他说得不对，正确的做法是：由222acb知90B，故3sin5aAb，因此应该选C．师：正确，这是一道陷阱题，常规90C，而本题条件暗示90B，所以今后注意审题要仔细．2．RtABC中，斜边AB的长为m，40B，则BC边长是（）A.sin40mB.cos40mC.tan40mD.tan40m生9：选B，理由：cos40BCAB可得cos40BCm，故选B．师：很好．3．ABC中，190,tan3CA，则sinB的值是（）A.1010B.23C.34D.31010生10：构造RtABC，由1tan3BCAAC可设,3BCkACk，从而10ABk，3310sin1010ACkBABk，所以选D．师：事实上，本题构造直角三角形后，可以用“特值法”，直接设1,3BCAC即可，原