[toán 11]pt lượng giác

S

sasani

[TEX]2(cosx+cos3x)-1-2cos2x=0 \\\Leftrightarrow 4cos2x.cosx -1-2cos2x=0 \\ \Leftrightarrow 4cosx(2cos^2x-1) -1 -2(2cos^2x-1)=0 \\ \Leftrightarrow 8cos^3x-4cos^2x-4cosx +1=0 [/TEX]
 
K

kakashi_hatake

2
$\sin 2x (\cos 2x -\cos 4x) + \cos 2x (\cos 2x+\cos 4x)=1 \leftrightarrow \sin 2x. \cos 2x - \sin 2x \cos 4x + \cos^2 2x -1+\cos 2x.\cos 4x=0 \\ \leftrightarrow \cos 4x(\cos 2x - \sin 2x) +\sin 2x (\cos 2x-\sin 2x)=0 \\ \leftrightarrow (\cos 4x +\sin 2x)(\cos 2x-\sin 2x)=0 $
 
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