Sagot :
[tex]\left\{\begin{array}{ccc}-\frac{5}{7}-\frac{11}{7}x=-y&/\cdot(-1)\\2y=7+5x\end{array}\right\\\left\{\begin{array}{ccc}\frac{5}{7}+\frac{11}{7}x=y\\2y=7+5x\end{array}\right\\\\substitute\\\\2\cdot\left(\frac{5}{7}+\frac{11}{7}x\right)=7+5x\\\\\frac{10}{7}+\frac{22}{7}x=7+5x\ \ \ /\cdot7\\\\10+22x=49+35x\\\\22x-35x=49-10\\\\-13x=39\ \ \ /:(-13)\\\\x=-3[/tex]
[tex]\left\{\begin{array}{ccc}x=-3\\y=\frac{5}{7}+\frac{11}{7}x\end{array}\right\\\left\{\begin{array}{ccc}x=-3\\y=\frac{5}{7}+\frac{11}{7}\cdot(-3)\end{array}\right\\\left\{\begin{array}{ccc}x=-3\\y=\frac{5}{7}-\frac{33}{7}\end{array}\right\\\left\{\begin{array}{ccc}x=-3\\y=-\frac{28}{7}\end{array}\right\\\left\{\begin{array}{ccc}x=-3\\y=-4\end{array}\right[/tex]
[tex]\left\{\begin{array}{ccc}x=-3\\y=\frac{5}{7}+\frac{11}{7}x\end{array}\right\\\left\{\begin{array}{ccc}x=-3\\y=\frac{5}{7}+\frac{11}{7}\cdot(-3)\end{array}\right\\\left\{\begin{array}{ccc}x=-3\\y=\frac{5}{7}-\frac{33}{7}\end{array}\right\\\left\{\begin{array}{ccc}x=-3\\y=-\frac{28}{7}\end{array}\right\\\left\{\begin{array}{ccc}x=-3\\y=-4\end{array}\right[/tex]