[tex]\displaystyle\bf\\1)\\\\+\left \{ {{3x-7y=11} \atop {6x+7y=16}} \right. \\---------\\9x=27\\\\x=3\\\\7y=3x-11=3\cdot 3-11=9-11=-2\\\\y=-\frac{2}{7}\\\\\\Otvet \ : \ \Big(3 \ ; \ -\frac{2}{7} \Big)\\\\2)\\\\\left \{ {{4x+2y=5} \atop {4x-6y=-7} \ |\cdot (-1)} \right. \\\\\\+\left \{ {{4x+2y=5} \atop {-4x+6y=7}} \right.\\----------\\8y=12\\\\y=1,5\\\\4x=5-2y=5-2\cdot 1,5=5-3=2\\\\x=2:4=0,5\\\\Otvet \ : \ (0,5 \ ; \ 1,5)}[/tex]

[tex]\displaystyle\bf\\3)\\\\\left \{ {{2x-3y=8} \ |\cdot(-7)\atop {7x-5y=-5} \ |\cdot 2} \right. \\\\\\+\left \{ {{-14x+21y=-56} \atop {14x-10y=-10}} \right. \\------------\\11y=-66\\\\y=-66:11=-6\\\\2x=3y+8=3\cdot (-6)+8=-18+8=-10\\\\x=-10:2=-5\\\\Otvet \ : \ (-5 \ ; \ -6)[/tex]