正欲弦定理解题 :三角形ABC中,设A>B>C,且A=2C,b=4,a+c=8,求a和c的值...
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答:由正弦定理得:sinA/a=sinC/c,∵A=2C,∴sin2C/sinC=a/c,cosC=a/2c;由余弦定理得:c²=a²+b²-2abcosC=a²+b²-a²b/c,a+c