[tex]f:\mathbb{R} \rightarrow \mathbb{R}, \quad f(1+x) = -2x-3 \\ \\ (\text{Facem: } 1+x \rightarrow t \Rightarrow x \rightarrow t-1) \\ \\ \begin{array}{rcl} \Rightarrow f(t) &=& -2\cdot (t-1)-3 \\ &=& -2t+2-3 \\ &=& -2t-1 \end{array} \\ \\ \Rightarrow \boxed{f(x) = -2x-1}[/tex]
