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Trả lời:
$450^o<x<540^o$
$\dfrac{5\pi}{2}<x<3\pi$
$⇒\dfrac{\pi}{2}<x<\pi$
$⇒\cos x<0$
Ta có:
$\sin x=\dfrac{1}{2}$
$⇒\cos^2 x=1-\dfrac{1}{4}=\dfrac{3}{4}$
$⇒\cos x=-\dfrac{\sqrt{3}}{2}$
$⇒\tan x=\dfrac{\sin x}{\cos x}=-\dfrac{\sqrt{3}}{3}$
$⇒\cot x=\dfrac{1}{\tan x}=-\sqrt{3}$.