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△ABC中∵sin(B+A)=2sin(B+C)∴sinC=2sinA为什么?
人气:469 ℃ 时间:2020-05-17 20:58:07
解答
∵B+A+C=π
sin(B+A)=2sin(B+C)
∴sin(B+A)=sin(π-C)=sinC
2sin(B+C)=2sin(π-A)=2sinA
∴sinC=2sinA
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