[tex]\displaystyle 1)\left \{ {{x-y=1} \atop {x+3y=9}} \right. \\\\(x-y)-(x+3y)=1-9\\-4y=-8\\y=2\\x-2=1\\x=3\\(x,y)=(3,2)\\\\2)\left \{ {{4x-6y=18} \atop {2x+y=1}} \right. \\\\\left \{ {{4x-6y=18} \atop {y=1-2x}} \right. \\\\4x-6(1-2x)=18\\\\x=\frac{3}{2}\\ \\y=1-2*\frac{3}{2}\\ \\y=-2\\\\(x,y)=(\frac{3}{2},-2)\\ \\3)\left \{ {{4x+5y=6} \atop {4x+3y=2}} \right. \\\\(4x+5y)-(4x+3y)=6-2\\2y=4\\y=2\\4x+5*2=6\\x=-1\\(x,y)=(-1,2)[/tex]