|A|是个范德蒙的行列式,
http://baike.baidu.com/picture/4567894/4567894/0/472309f7905298227a5938e5d5ca7bcb0a46d4a9?fr=lemma&ct=single#aid=0&pic=472309f7905298227a5938e5d5ca7bcb0a46d4a9
其中几个元素分别为a1=-1,a2=x,a3=3,a4=2x
所以|A|=(2x-3)(2x-x)(2x+1)(3-x)(3+1)(x+1)= -4x(x+1)(x-3)(2x+1)(2x-3)=0
共有5个相异实数根