Phương trình lượng giác cơ bản
\(sinx=sina \leftrightarrow\) \(\left[\begin{matrix} x= \alpha +k2\pi\\ x=\pi -\alpha + k2\pi \end{matrix}\right.\), \(k \in Z\)
\(cos x =cos \alpha \leftrightarrow \)\(\left[\begin{matrix} x= \alpha +k2\pi\\ x= -\alpha + k2\pi \end{matrix}\right.\)\(k \in Z\)
\(tanx=tan\alpha \leftrightarrow\)\(x=\alpha +k\pi, k\in Z\)
\(cotx=cot\alpha \leftrightarrow x=\alpha+k\pi, k\in Z\)
* Trường hợp đặc biệt
\(sinx=1 \leftrightarrow x=\frac{\pi}{2}+k2\pi\)
\(sinx=-1 \leftrightarrow x=-\frac{\pi}{2}+k2\pi\)
\(sinx=0\leftrightarrow x=k\pi\)
\(cosx=1\leftrightarrow x=k2\pi\)
\(cosx=-1\leftrightarrow x=\pi +k2\pi\)
\(cosx=0\leftrightarrow x=\frac{\pi}{2}+k\pi\)
\(tanx=1\leftrightarrow x=\frac{\pi}{4}+k\pi\)
\(tanx=-1\leftrightarrow x=-\frac{\pi}{4}+k\pi\)
\(tanx=0 \leftrightarrow sinx=0 \leftrightarrow x=k\pi\)
\(cotx=1\leftrightarrow x=\frac{\pi}{4}+k\pi\)
\(cotx=-1\leftrightarrow x=-\frac{\pi}{4}+k\pi\)
\(cotx=0 \leftrightarrow cosx=0 \leftrightarrow x=\frac{\pi}{2}+k\pi\)
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