f(x)=x^2*log(4)a( (4)表对数的底)
则f(x-1)+2x
=(x-1)^2*log(4)a+2x
=log(4) a*x^2+[2-2log(4) a]x+log(4) a
=0
当a=1时,log(4) a=0,则x=0,不符；
当a不等于1时,判别式=[2-2log(4) a]^2-4[log(4) a]^22