This is expression for $\tan(a+b+y)$
$$\frac{\tan(a)+\tan(b)+\tan(y)−\tan(a)\tan(b)\tan(y)}{1− \tan(a)\tan(b)−\tan(a)\tan(y)−\tan(b)\tan(y)}$$
I want to represent this with only $\tan(a)$, $\tan(b)$ and $\tan(y)$.
Clearly,I want to replace $1$ with tan functions of these three variables.
I need this answer because thie is from GelfAndSaul Trigonometry Book questions.Pg-145