1,Cho $\Delta $ABC. Chứng minh rằng:$\cos A\cos B\cos C \leq \sin \frac{A}{2}\sin \frac{B}{2}\sin \frac{C}{2}$
Trả lời 16-04-16 06:53 AM
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Nhận dạng $\triangle ABC$ biết $cosAcosBcosC=sin\frac{A}{2}sin\frac{B}{2}sin\frac{C}{2}$
Trả lời 18-04-16 11:48 PM
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a)$ -\sin3x +2\sin^2 \frac{3x}{2}+2 \sin2x =0$b) $ \sin^6 x+\cos^6 x =\frac{-7}{16} \tan \left(x-\frac{\pi}{3}\right) \tan \left(x+\frac{\pi}6\right)$c) $\sin \left(7x-\frac{5\pi}6\right)+\cos \left(3x-\frac{\pi}3\right)=0$d) $ \sin (\pi \cos x) =1$
Trả lời 18-06-16 06:19 PM
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a)$ -\sin3x +2\sin^2 \frac{3x}{2}+2 \sin2x =0$b) $ \sin^6 x+\cos^6 x =\frac{-7}{16} \tan \left(x-\frac{\pi}{3}\right) \tan \left(x+\frac{\pi}6\right)$c) $\sin \left(7x-\frac{5\pi}6\right)+\cos \left(3x-\frac{\pi}3\right)=0$d) $ \sin (\pi \cos x) =1$
Trả lời 18-06-16 08:12 PM
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1. m là một số cho trước, chứng minh rằng nếu: m.sin(a + b)
= cos(a - b)
Trong đó a - b khác k
Trả lời 08-04-16 07:06 PM
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$sinA+sinB+sinC\leq \frac{3\sqrt{3}}{2}$mình cần nhiều cách giải
Trả lời 09-04-16 01:03 PM
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Cho $\frac{sin^{4}x}{m}+\frac{cos^4x}{n}=\frac{1}{m+n}$Tính $\frac{sin^{10}x}{m}+\frac{cos^{10}x}{n}$
Trả lời 20-04-16 08:17 PM
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a ) $2\cos x(1-\cos 2x)$+$\sin 2x$=$1+2\sin x$b) $2\sin^2 2x-\cos 7x-1$=$\cos x$c) $ \tan x(2x-\pi/4)$$\tan (2x+\pi/4)$=$\frac{4\cos^2 2x}{\tan x-\cot x}$
Trả lời 16-06-16 09:38 PM
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a ) $2\cos x(1-\cos 2x)$+$\sin 2x$=$1+2\sin x$b) $2\sin^2 2x-\cos 7x-1$=$\cos x$c) $ \tan x(2x-\pi/4)$$\tan (2x+\pi/4)$=$\frac{4\cos^2 2x}{\tan x-\cot x}$
Trả lời 16-06-16 09:53 PM
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Chứng minh rằng $\frac{sin^{4}x - cos^{4}x + cos^{2}x }{2(1-cosx)} = cos^{2}\tfrac{x}{2}$
Trả lời 02-05-16 10:41 AM
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$P=\frac{sina}{cosa.cos2a}+\frac{sina}{cos2a.cos3a}+\frac{sina}{cos3a.cos4a}+...+\frac{sina}{cos(n.a).cos[(n+1)a]}$
Trả lời 03-05-16 03:51 PM
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a)$ -\sin3x +2\sin^2 \frac{3x}{2}+2 \sin2x =0$b) $ \sin^6 x+\cos^6 x =\frac{-7}{16} \tan \left(x-\frac{\pi}{3}\right) \tan \left(x+\frac{\pi}6\right)$c) $\sin \left(7x-\frac{5\pi}6\right)+\cos \left(3x-\frac{\pi}3\right)=0$d) $ \sin (\pi \cos x) =1$
Trả lời 18-06-16 07:12 PM
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a ) $2\cos x(1-\cos 2x)$+$\sin 2x$=$1+2\sin x$b) $2\sin^2 2x-\cos 7x-1$=$\cos x$c) $ \tan x(2x-\pi/4)$$\tan (2x+\pi/4)$=$\frac{4\cos^2 2x}{\tan x-\cot x}$
Trả lời 16-06-16 10:04 PM
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Trả lời 14-06-16 08:14 PM
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cho $a, b, c$ là các số với $\left| {a} \right|,\left| {b} \right|,\left| {c} \right|\leq 1$chứng minh rằng, nếu $a, b,c$ thỏa mãn: $a^{2}+b^{2}+c^{2}=1-2abc$ thì$a+b+c=2\sqrt{\frac{(1-a)(1-b)(1-c)}{2}}+1$
Trả lời 30-04-16 05:49 PM
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