解方程组 2x-y=-3 ①4x+5y=1 ② 3x-y=7① 5x+2y=8② 7x+5y=3① 2x-y=-4②

2x-y=-3 ①4x+5y=1 ②2x-y=-3 ①4x+5y=1 ②②-2*①得 7y=7 解得y=1代入y,得x=-1因此 x=-1 y=13x-y=7① 5x+2y=8② 3x-y=7 ①5x+2y=8 ②3*②-5*①得 11y=-11 解得y=-1代入y,得x=2因此 x=2 y=-17x+5y=3① 2x-y=-4②7x+5...