Pt lượng giác

T

tranvanhung7997

$cot 2x = cot (x + \dfrac{\pi}{2})$
<=> $cot 2x = tan (-x) = - tan x$
<=> $\dfrac{cos 2x}{sin 2x} = - \dfrac{sin x}{cos x}$
<=> $cos 2x . cos x + sin 2x . sin x = 0$
<=> $cos (2x - x) = 0$
<=> $cos x = 0$
<=> $x = \dfrac{\pi}{2} + k. \pi$
 
S

sasani


[TEX]cot 2x = cot (x + \frac{\pi}{2}) \\ 2x = x + \frac{\pi}{2} + k\pi \\ x = \frac{\pi}{2} + k\pi[/TEX]

PTLG cơ bản mà?!?!?!
 
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