（3xy-2x²+1/2y²）（3xy+2x²-1/2y²）=[3xy-(2x²-1/2y²)][3xy+(2x²-1/2y²)]=(3xy)²-(2x²-1/2y²)²=9x²y²-(4x^4-2x²y²+1/4y^4)=11x&...