Sagot :
1) x-y = 10 et 3x = y
2) [tex] \left \{ {{x-y = 10} \atop {3x = y}} \right. [/tex]
[tex] \left \{ {{x-y = 10} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{(y/3)-y = 10} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{(y/3)-(3y/3) = 10} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{-(2y/3) = 10} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{-2y = 30} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{y = -15} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{y = -15} \atop {x = -15/3}} \right. [/tex]
[tex] \left \{ {{y = -15} \atop {x = -5}} \right. [/tex]
2) [tex] \left \{ {{x-y = 10} \atop {3x = y}} \right. [/tex]
[tex] \left \{ {{x-y = 10} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{(y/3)-y = 10} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{(y/3)-(3y/3) = 10} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{-(2y/3) = 10} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{-2y = 30} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{y = -15} \atop {x = y/3}} \right. [/tex]
[tex] \left \{ {{y = -15} \atop {x = -15/3}} \right. [/tex]
[tex] \left \{ {{y = -15} \atop {x = -5}} \right. [/tex]