当A>0 A<1 (x^2-4)>3x当A》1(x^2-4)《3x
当a>1时,x^2-4<=3x解得-1<=x<=4当0=3x, 解得-1>=x或者x>=4
首先x^2-4>0且3x>0.解得x>2;0=3x; 解得-1<=x<=4, 故2a>1时:x^2-4<=3x; 解得x<=-1或x>=4, 故x>=4.