2022年山西英语周报chuz答案

17.(1)若选①由已知及正弦定理得,v3sinAcosA=sinA(sinBcosC+sin CcosB)∴3 sinAcosA= sarAsin(B+C),即√3 osasuna=sin2A,A∈(0,m),sinA≠0,nA=3,A=3(5分)若选②:由已知及倍角公式得(1-2 sin A)+2 sin B-1=2sinC(sinB-sinC)2 sin B-2 sin'A=2sinCsinB-2 sin'C,BWsin'B+sin'C-sin'A=sinCsinB,由正弦定理得b+c2-a2=bc,由余弦定理得coAb2+d2-d2=1,又A∈(0,n),∴A=3.(5分)若选③:由已知及正弦定理得(2sinB-sinC)cosA= sinAcom,2sin BcosA=sin(A+C)=sinBB∈(0),sB∴oMA=t,又A∈(0,x),A=,(5分)(2)由余弦定理a2=b2+2-2 2bccosa,a=2,A=3,得4=b2+c2-b,即(b+c)2-3bc=4.b+c=√10,∴b=2,S2.(12分

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