7. Let $y=f(x)$ be a strictly monotonically increasing function, and its inverse function be $y=g(x)$. Let $x_{1}, x_{2}$ be the solutions of the equations $f(x)+x=2$ and $g(x)+x=2$, respectively, then $x_{1}+x_{2}=$ $\qquad$ .
Let $f\left(x_{1}\right)=x_{2}$, then $g\left(x_{2}\right)=x_{1}$. Substituting into the equation, we get $\left\{\begin{array}{l}f\left(x_{1}\right)+x_{1}=x_{1}+x_{2}=2 \text {, } \\ g\left(x_{2}\right)+x_{2}=x_{1}+x_{2}=2 \text {. }\end{array}\right.$
Also, $y=f(x)$ is a strictly increasing function, and $x_{1}, x_{2}$ are the unique solutions to the equation, so $x_{1}+x_{2}=2$.