f[g(x)]=f(2x-1)=3(2x-1)^2+1=3(4x^2-4x+1）+1=12x^2-12x+4g[f(x)]=g(3x^2+1)=2(3x^2+1)-1=6x^2+1
f[g(x)]=3(2x-1)^2+1g[f(x)]=2(3x^2+1)-1
