[tex]\displaystyle\bf\\\left \{ {{3x-5y=8} \atop {x+y=0}} \right. \\\\\\\left \{ {{y=-x} \atop {3x-5\cdot(-x)=8}} \right. \\\\\\\left \{ {{y=-x} \atop {3x+5x=8}} \right. \\\\\\\left \{ {{y=-x} \atop {8x=8}} \right. \\\\\\\left \{ {{y=-x} \atop {x=8:8=1}} \right. \\\\\\\left \{ {{x=1} \atop {y=-1}} \right. \\\\\\Otvet \ : \ (1 \ ; \ -1)[/tex]