3x+4y=2 (1)2x-y=5 (2)(1)+(2)*43x+8x=2211x=22x=2y=-1将x=2 y=-1 代入 ax+b/2y=5与a/3-by=4得 2a-b/2=5 (1)a/3+b=4 (2)(1)*2+(2)4a+a/3=1413a/3=14a=42/13b=4-a/3=4-14/13=38/13