Let $\mathrm{f}(x)=\frac{a x}{x+1}, x \neq-1$, then for $\alpha=$ ________, $\mathrm{f}(\mathrm{f}(x))=x$.

The domain of definition of the function $y(x)$ is given by the equation $2^x+2^y=2$, is

The domain of definition of the function $f(x)$ given by the equation $2^x+2^y=2$ is

If $\mathrm{f}(x)=\frac{x}{2-x}, \mathrm{~g}(x)=\frac{x+1}{x+2}$, then (gogof) $(x)=$