8x + 9y = 17,x - 3y = -2,这个方程组,x - 3y = -2,3x - 9y = -6,3x - 9y + 8x + 9y = -6 + 17,11x = 11,x = 1,x - 3y = -2,1 - 3y = -2,3 - 3y = 0,1 - y = 0,y = 1,解方程组,x = 1,y = 1,
由x-3y=-2得:x=3y-2将x=3y-2带入8x+9y=17得y=1