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题 在△ＡＢＣ中 ,求证1 -ｃｏｓＡ1 -ｃｏｓＢ·ｃｏｓＣ+1 -ｃｏｓＢ1 -ｃｏｓＡ·ｃｏｓＣ+1 -ｃｏｓＣ1 -ｃｏｓＡ·ｃｏｓＢ≥ 2等号当且仅当△ＡＢＣ为正三角形时成立。 (注 供题人对第一位完整且正确的解答者授予奖金 5 0元 )。擂题 ( 52 )解答的评注(评注人 :郭?
In △ABC, verify that 1 -cosA1 -cosB·cosC+1 -cosB1 -cosA·cosC+1 -cosC1 -cosA·cosB≥ 2 equal signs holds if and only if △ABC is a regular triangle. (Note that the title person awards the first complete and correct answerer with a bonus of 50 yuan). The commentary to the question (52). (Commentary: Guo?