原式=(3x+1)^2 (3x-1)^2+(2x+1)(2x-1)
=(3x+1)^2 (3x-1)^2+4x^2-1
=(9x^2+1+6x)(9x^2+1-6x)+4x^2-1
=81x^4-54x^3+9x^2+9x^2-6x+1+54x^3-36x^2+6x+4x^2-1
=81x^4-14x^2