If $F\left(x\right)$ and $G\left(x\right)$ are even and odd extensions of the functions $f\left(x\right)=x\left|x\right|+\sin \left|x\right|+x{e}^x,$ where $x\in (0, 1)$, $g\left(x\right)=$$\cos \left|x\right|+x^2-x,$ where $x\in (0, 1)$ respectively to the interval $(-1, 0)$, then $F\left(x\right)+G\left(x\right)$  in $(-1, 0)$ is: