最新人教版八年级上册数学公开课《因式分解课件PPT》课件ppt.ppt 36页

'人教版八年级上册数学公开课《因式分解课件PPT》 请把下列多项式写成整式的乘积的形式:(1)x2+x=(2)x2–1探究整式的乘法用前面所学知识填空:x(x+1)=；(x+1)(x－1)=.x2+xx2－1回忆x(x+1)=(x+1)(x-1) x2-1因式分解整式乘法(x+1)(x-1)因式分解与整式乘法是相反方向的变形定义：上面我们把一个多项式化成了几个整式的积的形式,像这样的式子变形叫做把这个多项式因式分解,也叫做把这个多项式分解因式. 找一找：下列个多项式的公因式是什么？(1)3x+6y(2)ab-2ac(3)a2-a3(4)4(m+n)+2(m+n)(5)9m2-6mn(6)-6x2y-8xy22aa22(m+n)3m-2xy 例1把8a3b2+12ab3c分解因式.解:8a3b2+12ab3c=4ab2•2a2+4ab2•3bc=4ab2(2a2+3bc). 例2把2a(b+c)-3(b+c)分解因式.分析:(b+c)是这个式子的公因式,可以直接提出.解:2a(b+c)–3(b+c)=(b+c)(2a-3). 诊断：小明解得有误吗？（1）把12x2y+18xy2分解因式解：原式=3xy（4x+6y）（2）把3x2-6xy+x分解因式解：原式=x(3x-6x)（3）把-x2+xy-xz分解因式解：原式=-x(x+y-z)注意:1.公因式要提尽2.某项提出莫漏13.首项有负常提负 1、3mx-6my2、x2y+xy23、12a2b3－8a3b2－16ab44、－5a2b+15ab2 巧妙计算:1.13.8x0.125+86.2x1/82.已知a+b=5,ab=3,求a2b+ab2得值3.计算5×34+24×33+63×32. 智力抢答(1)259x1/3+259x1/5+259x7/15(2)992+99 小结：1、什么叫因式分解？2、确定公因式的方法：（1）定系数（2）定字母（3）定指数3、提公因式法分解因式的步骤（分两步）：第一步，找出公因式；第二步，提取公因式；4、提公因式法分解因式应注意的问题：（1）公因式要提尽；（2）某项提出莫漏1；（3）首项有负常提负，提出负号时要注意变号 综合闯关：1、计算（-2）101+（-2）1002已知，2x+y=4,xy=3,求代数式2x2y+xy2的值 YoungGoodmanBrown NathanielHawthorneHewasborninSalem,Massachusetts.SomeofhisancestorsweremenofprominenceinthePuritanTheocracyof17thcenturyNewEngland.YoungHawthornewasintenselyawareofthemisdeedsofhisPuritanancestors,andthisawarenessledtohisunderstandingofevilbeingatthecoreofhumanlife,to“theblacknessinHawthorne”,asHermanMelvilleputit.Hawthornewrotesomebooksasanattemptatexpiatingthesinofhisancestors. Readinghistalesandromances,onecannotbutbeoverwhelmedbythe“black”visionwhichtheseworksreveal.ItillustratestosomeextenttheinfluencethattheCalvinistdoctrineof“originalsinandtotaldepravityhaduponhismind. PlotYoungGoodmanBrownbeganhisstoryatsunsetinSalem,Massachusetts,leavinghisyoungwifeFaithtojoininanunspecifiedbutobviouslyunholyritual.HemetmanypeoplealongthewayandmanyofthemwerehistownfolkwhomhehadconsideredexemplaryChristians,includinghisminister,deacon,thewomanwhotaughthimcatechismandevenhisvirginwife. Theceremonybegansomewheredarkanddeepinsidetheforest.Thenextmorning,BrowncameslowlyintothestreetofSalemwherehebumpedintothepeoplehehadmetalongthewaytotheritual.Deeplyshakenbywhathehadseen,Brownbegantoholdasuspiciousandcynicalattitudetowardthemincludinghiswife. Tosumup,thestorytellBrown’scollapseofFaith. SymbolsSunsetPinkribbonsForestFaithGoodmanBrownThesnakelikestickSalem SunsetAsweknow,thestoryhappenedatsunsetwiththedevelopmentatnight.Sunsetisthesarting-pointofnightwhichsignifiesecilandarisepeople’sfearofunknown.Theauthorchosesuchatimeforthepurposeofbuildinguphorrificatmosphereandwhat’smore,ofdemonstratingthedarksideofthenatureofhumanbeings. PinkRibbonsAccordingtoBible,redrepresentsevilwhilewhiterepresentsholiness.Andthecolorofribbonsispink-betweenredandwhite.OtonlydothepinkribbonsrepresentweosidesofFaith-purityandkindnessasawifeandevilaasonewhojoinedinsucharitual,butalsorepresentBrown’sreligiousbelief. Atthebeginningofthestory,Faithwhoworesuchacaptrieddetainherhusband,whichalsomeantVrowntriedtotemporallyabnegatehisreligiousbelieftoleavefortheevilparty. FaithThisnameisrepeatedthroughoutthewholestory.Atthebeginningofthestory,Brownputhisheadback,aftercrossingthethreshold,toexchangeapartingkisswithhisyoungwife.AndFaith,asthewifewasaptlynamed… Andwhenheenteredtheforestandmetthecompanion,hesaid”Faithkeptmebackawhile.” Faithiscomprehendedintwoways.OnewayisthattherecentlymarriedwifeFaithBegrudginglylethimjointheritualandtheotheroneisthatVrown’sreligiousbeliefmadehimhesitatedbeforehisdeparture. ThestoryhappensinSlemvillagewhereandwhennecromancywasverypopular.Atthattime,peoplefromofficialstocommononeswereallcaptivatedbynecromancy.Bysettingthehistoricalbackgroundof“Salemwitchtrals”,writersuccessfullyprovidedthereaderswithasenseofrealityandlettehmbelievethatthestorymighthavebeendericedfomwhathadreallyhappenedbefore,thuspulledhisstorytothemnearerandmadethemmoredevoted. YoungGoodmanBrownItisveryintelligentofHawthornetochoosethisnameasitisapun.Itrevealsaimagetousthattheheroisayouthfulmanofvirtue.Plus,Brownisapopularnameasitcanrepresent“Everyman”. TheSnake-likeStickWhenBrownwalkedinthedarkforest,hemetanoldmanwhocameoutsuddenlywithastick“whichborethelikenessofagreatblacksnake,socuriouslywroughtthatitmightalmostbeseentotwistandwriggleitselflikealivingserpent.”TheserpentstickmakesusthinkoftheimageofSatanintheBible.Itsymbolizesevilseduction. Forest“…adearyroaddarkenedbyallthegloomiesttreesoftheforest,whichbarelystoodasidetoletthenarrowpathcreepthrough,andclosedimmediatelybehind.Itwasallaslonelyascouldbe…”“theremaybeadevilishIndianbehindeverytree” Theforestsymbolizesthedarkevilforce,whichindicatesman’sfearfulnaturetowardsthemysteriousandtheunknown. ThemeThestoryuncoverstheinherentevilandsinofhumanity.HawthornehadsetalastingecampleinAmericanLiteratureofcombiningmoraldiscussionwithhighlyartisticrepresentationjustaswecanseefromthisstory.HawthorneusedBrown’sexperiencetoenlightenpeopletobebraveandfacealltheevilinlifewithanopen HawthorneusedBrown’sexperiencetoenlightenpeopletobebraveandfacealltheevilinlifewithanopenheart,sothatonecouldgrowupinahealthywayandbecomemorematureandgivepositivemeaningtolife,sothatpeoplecouldavoidBrown-destroying. TheConclusionThePuritanismitselfasauniquehistoricalphenomenonplaysasignificantroleinthedevelopingofAmericanliterature.ThroughtHawthorne’scomplex,contradictoryreligiousviews,thethemeofhisdepravityofthePuritanismandthe“orginalsin”,alsoitreflectedthatthepruitansuppressanddestructtothehumanbeings.Thiswasaspecialnesswithwhichhisfamilyandsocialbackgroundwasinseparable.'