Giải phương trình: $2\cos^2\frac{x^2+x}{2}=2^x+2^{-x}$.
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Cho : 2.cos2x -3 cosx -3 >0, chứng minh rằng: sin (1/cosx) < 0
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Cho tam giác ABC không tù . CMR : $\tan \frac{A}{2}$ + $\tan \frac{B}{2} $$ + \tan \frac{C}{2}$ + $\tan \frac{A}{2}$$\tan \frac{B}{2}$$\tan \frac{C}{2}$ $\geq $ $\frac{10\sqrt{3}}{9}$
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Cho $\frac{\sin \alpha+\sin \beta+\sin \gamma }{\sin(\alpha+\beta+\gamma)}=\frac{\cos\alpha+\cos\beta+\cos\gamma}{\cos(\alpha+\beta+\gamma)}=m$Tìm $\min P=\cos^n(\alpha+\beta)+cos^n(\beta+\gamma)+cos^n(\gamma+\alpha)$ với $n\in Z;n\ge2$
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Cho $\frac{\sin \alpha+\sin \beta+\sin \gamma }{\sin(\alpha+\beta+\gamma)}=\frac{\cos\alpha+\cos\beta+\cos\gamma}{\cos(\alpha+\beta+\gamma)}=m$Tìm $\min P=\cos^n(\alpha+\beta)+cos^n(\beta+\gamma)+cos^n(\gamma+\alpha)$ với $n\in Z;n\ge2$
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Cho $\frac{\sin \alpha+\sin \beta+\sin \gamma }{\sin(\alpha+\beta+\gamma)}=\frac{\cos\alpha+\cos\beta+\cos\gamma}{\cos(\alpha+\beta+\gamma)}=m$Tìm $\min P=\cos^n(\alpha+\beta)+cos^n(\beta+\gamma)+cos^n(\gamma+\alpha)$ với $n\in Z;n\ge2$
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Cho $\frac{\sin \alpha+\sin \beta+\sin \gamma }{\sin(\alpha+\beta+\gamma)}=\frac{\cos\alpha+\cos\beta+\cos\gamma}{\cos(\alpha+\beta+\gamma)}=m$Tìm $\min P=\cos^n(\alpha+\beta)+cos^n(\beta+\gamma)+cos^n(\gamma+\alpha)$ với $n\in Z;n\ge2$
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Cho $\frac{\sin \alpha+\sin \beta+\sin \gamma }{\sin(\alpha+\beta+\gamma)}=\frac{\cos\alpha+\cos\beta+\cos\gamma}{\cos(\alpha+\beta+\gamma)}=m$Tìm $\min P=\cos^n(\alpha+\beta)+cos^n(\beta+\gamma)+cos^n(\gamma+\alpha)$ với $n\in Z;n\ge2$
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Cho $\frac{\sin \alpha+\sin \beta+\sin \gamma }{\sin(\alpha+\beta+\gamma)}=\frac{\cos\alpha+\cos\beta+\cos\gamma}{\cos(\alpha+\beta+\gamma)}=m$Tìm $\min P=\cos^n(\alpha+\beta)+cos^n(\beta+\gamma)+cos^n(\gamma+\alpha)$ với $n\in Z;n\ge2$
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Cho $\frac{\sin \alpha+\sin \beta+\sin \gamma }{\sin(\alpha+\beta+\gamma)}=\frac{\cos\alpha+\cos\beta+\cos\gamma}{\cos(\alpha+\beta+\gamma)}=m$Tìm $\min P=\cos^n(\alpha+\beta)+cos^n(\beta+\gamma)+cos^n(\gamma+\alpha)$ với $n\in Z;n\ge2$
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Cho $\frac{\sin \alpha+\sin \beta+\sin \gamma }{\sin(\alpha+\beta+\gamma)}=\frac{\cos\alpha+\cos\beta+\cos\gamma}{\cos(\alpha+\beta+\gamma)}=m$Tìm $\min P=\cos^n(\alpha+\beta)+cos^n(\beta+\gamma)+cos^n(\gamma+\alpha)$ với $n\in Z;n\ge2$
Trả lời 02-08-16 10:19 PM
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CHứng minh rằng $sinx+siny+sinz$ $\leq $ $3.sin$ $\frac{x+y+z}{3}$
Trả lời 04-05-16 08:55 PM
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cho tam giác $ABC$ thỏa mãn:$\frac{1}{\sin ^{a}A}+\frac{1}{\sin ^{b}B}+\frac{1}{\sin ^{c}C}\leq \frac{1}{\sqrt[x]{\cos \frac{A}{2}}}+\frac{1}{\sqrt[y]{\cos \frac{B}{2}}}+$$\frac{1}{\sqrt[z]{\cos \frac{C}{2}}}$ (với $a, b, c, x, y,z \in...
Trả lời 02-05-16 12:18 PM
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Chứng minh $\frac 1{\sin A}+\frac 1{\sin B}+\frac 1{\sin C} \ge \frac{1}{\cos \frac A2}+\frac 1{\cos \frac B2}+\frac 1{\cos \frac C2}$
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tam giác ABC sẽ có đặc điểm gì nếu....:$\frac{\sqrt[2016]{\sin A }+\sqrt[2016]{\sin B}+\sqrt[2016]{\sin C}}{\sqrt[2016]{\cos \frac{A}{2}}+\sqrt[2016]{\cos \frac{B}{2}}+\sqrt[2016]{\cos \frac{C}{2}}}=1$......................................................................
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giải pt lượng giác:$\frac{4sin^{2}2a}{1-cos^{2}a}=2$
Trả lời 13-04-16 08:29 PM
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CMR:$m_{a}.m_{b}.m_{c}\geq l_{a}.l_{b}.l_{c}$
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$\cos (\sin x) >\sin (\cos x)$
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$a) \cos A+\cos B+ \cos C \le \frac 32$$b) \cos2A+\cos 2B+\cos 2C \ge \frac{-3}2$$c)\sin \frac A2+\sin \frac B2+\sin \frac C2 \le \frac 32$$d) \cos A-\cos B + \cos C \ge \frac{-3}2$
Trả lời 27-01-16 10:55 PM
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$a) \cos A+\cos B+ \cos C \le \frac 32$$b) \cos2A+\cos 2B+\cos 2C \ge \frac{-3}2$$c)\sin \frac A2+\sin \frac B2+\sin \frac C2 \le \frac 32$$d) \cos A-\cos B + \cos C \ge \frac{-3}2$
Trả lời 26-01-16 10:44 PM
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