f(x)=ln(9+4x)+ln(9x-2)=ln[(9+4x)(9x-2)]in(f(x))=in{ln[(9+4x)(9x-2)]}=(9+4x)(9x-2)=36x^2+73x-18=(6x+73/12)^2-18-(73/12)^2反函数解析式为：x={[in(f(x))+18+(73/12)^2]^(1/2) -73/12}/6