摘要：在△ABC中常用的恒等式 (1)tanA+tanB+tanC=tanA·tanB·tanC (2)cotA·cotB+cotB·cotC+cotC·cotA=1 (3)tantan+tantan+tantan=1 (4)++=1 (5)sinA+sinB+sinC=4coscoscos (6)cosA+cosB+cosC=1+4sinsinsin

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