Chủ đề này có 1 trả lời

[phaidodaihoc1996]

$2cos6x+2cos4x-\sqrt{3}cos2x=sin2x+\sqrt{3}$

[mystery266]

$2cos6x+2cos4x-\sqrt{3}cos2x=sin2x+\sqrt{3}$

$2(cos6x+cos4x)=sin2x+\sqrt{3}(1+cos2x)$

 

$4.cos5x.cosx=2.sinx.cosx+\sqrt{3}(2cos^2{x})$

 

$\Rightarrow cosx=0\vee 4.cos5x=2.sinx+\sqrt{3}(2cos{x})$

 

$cos5x=\frac{1}{2}sinx+\frac{\sqrt{3}}{2}cos{x}$

 

$cos5x=cos(x-\frac{\pi}{6})$