Question
Find the general solution of $\cos \theta-\sin \theta=1$

Answer

Solution: We have $\cos \theta-\sin \theta=1$
$ \therefore \quad \frac{1}{\sqrt{2}} \cos \theta-\frac{1}{\sqrt{2}} \sin \theta=\frac{1}{\sqrt{2}}$
$\therefore \quad \cos \theta \cos \frac{\pi}{4}-\sin \theta \sin \frac{\pi}{4}=\frac{1}{\sqrt{2}}$
$\therefore \quad \cos \left(\theta+\frac{\pi}{4}\right)=\cos \frac{\pi}{4}$
$\therefore \quad \theta+\frac{\pi}{4}=2 n \pi \pm \frac{\pi}{4}$
$\therefore \quad \theta+\frac{\pi}{4}=2 n \pi-\frac{\pi}{4} \text { or } \theta+\frac{\pi}{4}=2 n \pi+\frac{\pi}{4}$
$\therefore \quad \theta=2 n \pi-\frac{\pi}{2} \text { or } \theta=2 n \pi, \text { where } n \in Z \text { is the required general solution. } $

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