## Giúp mình với ạ Cảm ơn M n trước ạ !

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Giúp mình với ạ
Cảm ơn M n trước ạ !

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1 year 2020-10-31T12:09:10+00:00 1 Answers 58 views 0

$\begin{array}{l} b){\cos ^2}x – 3\sin x – 3 = 0\\ \Rightarrow 1 – {\sin ^2}x – 3\sin x – 3 = 0\\ \Rightarrow {\sin ^2}x + 3\sin x + 2 = 0\\ \Rightarrow \left( {\sin x + 1} \right)\left( {\sin x + 2} \right) = 0\\ \Rightarrow \sin x = – 1\\ \Rightarrow x = – \dfrac{\pi }{2} + k2\pi \\ Vay\,x = – \dfrac{\pi }{2} + k2\pi \\ c)\cos 2x + 4\cos x – 5 = 0\\ \Rightarrow 2{\cos ^2}x – 1 + 4\cos x – 5 = 0\\ \Rightarrow 2{\cos ^2}x + 4\cos x – 6 = 0\\ \Rightarrow {\cos ^2}x + 2\cos x – 3 = 0\\ \Rightarrow \left( {\cos x – 1} \right)\left( {\cos x + 3} \right) = 0\\ \Rightarrow \cos x = 1\\ \Rightarrow x = \dfrac{\pi }{2} + k2\pi \\ Vay\,x = \dfrac{\pi }{2} + k2\pi \\ d)\cos 2x – \sin x – 1 = 0\\ \Rightarrow 1 – 2{\sin ^2}x – \sin x – 1 = 0\\ \Rightarrow 2{\sin ^2}x + \sin x = 0\\ \Rightarrow \sin x\left( {2\sin x + 1} \right) = 0\\ \Rightarrow \left[ \begin{array}{l} \sin x = 0\\ \sin x = – \dfrac{1}{2} \end{array} \right.\\ \Rightarrow \left[ \begin{array}{l} x = k\pi \\ x = \dfrac{{ – \pi }}{6} + k2\pi \\ x = \dfrac{{7\pi }}{6} + k2\pi \end{array} \right.\\ e)2\tan x – 2\cot x – 3 = 0\\ \Rightarrow 2\tan x – \dfrac{2}{{\tan x}} – 3 = 0\\ \Rightarrow 2{\tan ^2}x – 3\tan x – 2 = 0\\ \Rightarrow \left( {2\tan x + 1} \right)\left( {\tan x – 2} \right) = 0\\ \Rightarrow \left[ \begin{array}{l} \tan x = – \dfrac{1}{2}\\ \tan x = 2 \end{array} \right.\\ \Rightarrow \left[ \begin{array}{l} x = \arctan \left( { – \dfrac{1}{2}} \right) + k\pi \\ x = \arctan 2 + k\pi \end{array} \right. \end{array}$