(3y²+1/2x)(1/2x-3y²)=(1/2x+3y²)(1/2x-3y²)=(1/2x)²-(3y²)²=x²/4-9y⁴（x-1/2)（x+1/2）（x²+1/4）=(x²-1/4)（x²+1/4）=x⁴-1/16（x+y)(x-y)+（...