①｛x+2y= -2 ｛2x+4y= -4
｛7x-4y= -41 ｛7x-4y= -41 2x+4y+7x-4y=-45 9y=-45 y =-5 x=8
②｛17x-9y=61 ｛51x-27y=183
｛51x+13y=63 ｛51x+13y=63 51x-27y-51x-13y=120 y=-3 x=2
③ {x+y= -9 ③ {x+y= -9
｛1\3(x+y)-2y=3 ｛(x+y)-6y=9 x+y-x+5y=-18 y=-3 x=-6