ĐKXĐ:...
\(\Leftrightarrow tan\left(x-\frac{\pi}{4}\right)=-1\)
\(\Leftrightarrow x-\frac{\pi}{4}=-\frac{\pi}{4}+k\pi\)
\(\Leftrightarrow x=k\pi\)
Do \(-\pi< x< 5\pi\Rightarrow-\pi< k\pi< 5\Rightarrow k=\left\{0;1;2;3;4\right\}\)
Các nghiệm thỏa mãn: \(x=\left\{0;\pi;2\pi;3\pi;4\pi\right\}\)