了情1994
幼苗
共回答了23个问题采纳率:78.3% 举报
cosB/(cosA-2cosC)=b/(2c-a))=sinB/(2sinC-sinA)2sinCcosB-sinAcosB=sinBcosA-2sinBcosC2sin(B+C)=sin(A+B)2sinA=sinC2a=ca+b+c=53a+b=5b=5-3acosB=(a^2+c^2-b^2)/(2ac)=(a^2+4a^2-9a^2+30a-25)/(4a^2)=1/4-4a^2+30a-25=a^2a^2-6a+5=0(a-1)(a-5)=0a=1b=5-3a=2
1年前
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