giúp t vs m.n

N

nguyentrantien

123tuananh said:
[TEX]3cos(3x)cos(x)+\sqrt{3}(1+sin2x)=2\sqrt{3}cos^2(2x+\frac{pi}{4})[/TEX]
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[tex] \Leftrightarrow \frac{3}{2}(cos4x+cos2x)+\sqrt{3}+\sqrt{3}sin2x=2\sqrt{3}.\frac{1+cos(4x+\frac{\pi}{2})}{2}[/tex]
[tex] \Leftrightarrow 3(cos4x+cos2x)+2\sqrt{3}+2\sqrt{3}sin2x=2\sqrt{3}-2\sqrt{3}sin4x[/tex]
[tex] \Leftrightarrow 3(cos4x+cos2x)=-2\sqrt{3}(sin4x+sin2x)[/tex]
[tex] \Leftrightarrow 6cos3x.cosx=-4\sqrt{3}sin3x.cosx[/tex]
đến đây bạn tự giải nhá
 
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