2019-2020年高考数学复习第二轮解三角形专题复习教案

2019-202012ABCa2=b2+c2-2bccosbcacb2cos222RCcBbAa2sinsinsinA+B+C=180sin(A+B)=sinC,cos(A+B)=-cosC,cos2C=sin2BA,sin2C=cos2BAS=21absinC=21bcsinA=21casinBS=pr=))()((cpbpapp(p=2cba,r)a=bcosC+ccosBb=acosC+ccosAc=acosB+bcosA1ABCa=3,b=2,B=45A,CcsinA=23245sin3sinbBa,B=4590ba,A=60A=120(1)A=60,C=180-(A+B)=75c=22645sin75sin2sinsinBCb,(2)A=120,C=180-(A+B)=15c=22645sin15sin2sinsinBCb2ABC22tantanbaBAABCBABAAAABBA2sin2sinsinsincosAcosBsinsincossincossin222A=2B2A=1802BA=BA+B=90ABC22222222222222sincoscossinbaRbbcacbacbcaRabaBABAb2(a2+c2b2)=a2(b2+c2a2)(a2b2)(a2+b2c2)=0a=ba2+b2=c2ABC3ABCb=1,1a+c2.:CcBbAasinsinsin,a+c=Bbsin(sinA+sinC)=232(sinA+sinC)=332[sinA+sin(120A)]=2sin(A+30)0A12030A+30150,12sin(A+30)2.B=60,b=1a2+c2-b2=2accos60,a2+c2-1=ac,a2+c2-ac=1,(a+c)2+3(a-c)2=4,(a+c)2=4-3(a-c)2.0a-c103(a-c)23,4-3(a-c)24,(a+c)24,a+c2a+c1,1a+c2ORABCBbaCARsin2sinsin222ABCSbaBRBAR2sin2sinsin22222222babca222cos222abcbaC4cBARabCabSsinsin44242sin212BABARcoscos222BARcos22222A=B2max212RS5O())102arccos(300kmP20km/h4560km10km/h()Ox.th),(yxP.22201027300,2220102300tytx222)]([)()(tryyxx10)(trt+60tO,)6010()0()0(222tyx,)6010()22201027300()2220102300(222ttt0288362tt2412t.12()t(h)Q,10t+60(km)tO,6010tOQOPQPOPQPOPQOQcos2222PO=300,PQ=20t5445coscosOPQ222222300960020cos2tttOPQPOPQPOPQOQ22226010300960020tttt2412t1(,),nabnmnmmA.(,)(,)babaB.(,)abC.(,)(,)ababD.(,)ba211(1,),(0,),,22abcakbdabcd4kA.1B.C.12D.132,5,3abababA.23B.35C.23D.354RtABC2,ABACABBC=53ab75ab4ab72abab___________1A2A3C44560