Bonjour Mariame221
Formule générale : [tex]\boxed{u_n=u_0+n\times r}[/tex]
[tex]\left\{\begin{matrix}u_{6}=12\\u_{26}=4 \end{matrix}\right.\ \ \ \ \left\{\begin{matrix}u_0+6r=12\\u_0+26r=4 \end{matrix}\right.\ \ \ \ \left\{\begin{matrix}u_0=12-6r\\u_0+26r=4 \end{matrix}\right.[/tex]
[tex]\ \ \ \ \left\{\begin{matrix}u_0=12-6r\\12-6r+26r=4 \end{matrix}\right.\ \ \ \ \left\{\begin{matrix}u_0=12-6r\\20r=4-12 \end{matrix}\right.\ \ \ \ \left\{\begin{matrix}u_0=12-6r\\20r=-8 \end{matrix}\right.[/tex]
[tex]\ \ \ \ \left\{\begin{matrix}u_0=12-6r\\r=-\dfrac{8}{20}=-0,4 \end{matrix}\right.\ \ \ \ \left\{\begin{matrix}u_0=12-6\times(-0,4)\\r=-0,4 \end{matrix}\right.\ \ \ \ \left\{\begin{matrix}u_0=12+2,4\\r=-0,4 \end{matrix}\right.[/tex]
[tex]\ \ \ \ \boxed{\left\{\begin{matrix}u_0=14,4\\r=-0,4 \end{matrix}\right.}[/tex]
