Step-by-step explanation:
[tex] \tan( \frac{3\pi}{4}- x) = \frac{ \tan( \frac{3\pi}{4} ) - \tan(x) }{1 + \tan( \frac{3\pi}{4} ) \tan(x)} [/tex]
Since tan(3pi/4) = -1
[tex] \tan( \frac{3\pi}{4}- x) = \frac{ - 1 - \tan(x) }{1 - \tan(x)} [/tex]
[tex] = \frac{ \tan(x) + 1}{ \tan(x) - 1} [/tex]