x-y=a+3-----------------(1) 2x+y=5a-----------(2) (1)+(2),3x=6a+3 x=(6a+3)/运敏肢拿如3 (1)*2,2x-2y=2a+6-----------(3) (3)-(2),-3y=-3a+6, y=(-3a+6)/-3 x>0,y0 (-3a+6)/旁世-3
