$\Delta ABC$ là tam giác bất kì, chứng minh: $(1-cosA)(1-cosB)(1-cosC)\geq cosA.cosB.cosC$.
Dấu ' = ' xảy ra khi nào?
bđt: $(1-cosA)(1-cosB)(1-cosC)\geq cosA.cosB.cosC$
Started By online, 11-08-2012 - 21:32
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Posted 11-08-2012 - 21:32
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