a的平方（x-1）＜3a+x+2
x-1<(3a+2)/a^2+x/a^2
(1-1/a^2)x<1+(3a+2)/a^2
若a^2>1,即a>1或a<-1
则x<(a+1)(a+2)/(a^2-1)
x<(a+2)/(a-1)
x<1+3/(a-1)
若a^2<1,即-1x>(1+(3a+2)/a^2)/(1-1/a^2)
x>1+3/(a-1)
a=1或-1无解