Nghiệm của phương trình $\cos x = - \dfrac{1}{2}$ là:

\(x = \dfrac{\pi }{3} + k\pi \).

\(x = \dfrac{\pi }{2} + k2\pi \).

\(x =  - \dfrac{\pi }{6} + k\pi \).

\(x =- \dfrac{\pi }{3} + k\pi \).

\(x = k\pi \left( {k \in Z} \right)\)

\(x = \dfrac{\pi }{2} + k2\pi \left( {k \in Z} \right)\)

\(x = k2\pi \left( {k \in Z} \right)\)

\(x = \dfrac{\pi }{2} + k\pi \left( {k \in Z} \right)\)

\(\cos x \ne 1 \Leftrightarrow x \ne \dfrac{\pi }{2} + k\pi \left( {k \in Z} \right)\)

\(\cos x \ne 0 \Leftrightarrow x \ne \dfrac{\pi }{2} + k\pi \left( {k \in Z} \right)\)

\(\cos x \ne  - 1 \Leftrightarrow x \ne  - \dfrac{\pi }{2} + k2\pi \left( {k \in Z} \right)\)    

\(\cos x \ne 0 \Leftrightarrow x \ne \dfrac{\pi }{2} + k2\pi \left( {k \in Z} \right)\)

\(y = \cos x\)

 \(y = \sin x\)

\(y = \cot x\)

\(y = \tan x - 1\)

Hàm số không tuần hoàn

\({T_0} = 2\pi \)

\({T_0} = \pi \)

\({T_0} = 4{\pi ^2}\)

$x =  - \dfrac{\pi }{2} + k2\pi $.

$x = \dfrac{\pi }{2} + k\pi $.

$x = k\pi $.

$x = \dfrac{\pi }{2} + k2\pi $.