Giai pt

A

atulara

[TEX]\Leftrightarrow 2\cos ^2 \left(2\pi -x+\frac{\pi }{4} \right) - 2\cos ^2 x = 2\cos x - \frac{1}{\cos x} + \frac{1}{\cot x} \\ \Leftrightarrow \left[\sqrt{2}\cos \left(-x+\frac{\pi }{4} \right) \right]^2 - 2\cos ^2 x = 2\cos x - \frac{1}{\cos x} + \frac{\sin x}{\cos x} \\ \Leftrightarrow (\sin x + \cos x )^2 .\cos x - 2\cos ^2 x .\cos x - 2\cos ^2 x - \sin x + 1 = 0 \\ \Leftrightarrow \cos x + 2\sin x .\cos ^2 x - 2\cos ^2 x .\cos x - 2\cos ^2 x - \sin x + 1 = 0 \\ \Leftrightarrow \sin x (2\cos ^2 x -1) - \cos x (2\cos ^2 x -1) - (2\cos ^2 x -1) = 0 \\ \Leftrightarrow \cos 2x (\sin x - \cos x - 1) = 0[/TEX]
Đến đây bạn tự làm tiếp nhé :D
 
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