Cho ABC nhọn, chứng minh rằng :
1/ $cos\frac{A}{2}+cos\frac{B}{2}+cos\frac{C}{2}< 2(sin\frac{A}{2}+sin\frac{B}{2}+sin\frac{C}{2})$
2/ $1< \frac{sinA+sinB+sinC}{cosA+cosB+cosC}< 2$
$1< \frac{sinA+sinB+sinC}{cosA+cosB+cosC}< 2$
Started By Nhok Tung, 27-12-2015 - 20:33
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