Verified answer

[tex]\displaystyle\bf\\1)\\\\\left \{ {{2x+y=5} \atop {x-y=2}} \right. \\\\2)\\\\\left \{ {{2x+y=5} \atop {2x=5-y}} \right. \\\\3)\\\\\left \{ {{2x+y=5} \atop {-y=2x+3}} \right.[/tex]