Answer
$\dfrac{\tan x+1}{1-\tan x}$
Work Step by Step
In the given problem, the wrong formula is used because a mistake was made in the denominator.
Now we will write the correct formula.
$\tan (x+\dfrac{\pi}{4}) = \dfrac{\tan x+\tan \dfrac{\pi}{4}}{1-\tan x \tan \dfrac{\pi}{4}}$
or, $= \dfrac{\tan x+1}{1-\tan x}$
