Find the general solution of $\cos ec\, x=-2$
Find the general solution of $\cos ec\, x=-2$
$\cos ec\, x=-2$
It is known that
$\cos ec\, \frac{\pi}{6}=2$
$\therefore \cos ec \left(\pi+\frac{\pi}{6}\right)=-\cos ec\, \frac{\pi}{6}=-2$ and $\cos ec\, \left(2 \pi-\frac{\pi}{6}\right)=-\cos ec\, \frac{\pi}{6}=-2$
i.e., $\cos ec\, \frac{7 \pi}{6}=-2$ and $\cos ec\, \frac{11 \pi}{6}=-2$
Therefore, the principal solutions are $x=\frac{7 \pi}{6}$ and $\frac{11 \pi}{6}$
Now $\cos ec\, x=\cos ec\, \frac{7 \pi}{6}$
$\Rightarrow \sin x=\sin \frac{7 \pi}{6} \quad\left[\cos ec\, x=\frac{1}{\sin x}\right]$
$\Rightarrow x=n \pi+(-1)^{n} \frac{7 \pi}{6},$ where $n \in Z$
Therefore, the general solution is $x=n \pi+(-1)^{n} \frac{7 \pi}{6},$ where $n \in Z$.
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