(2x-3y)²-(4y-3x)(3x+4y)=4x²-12xy+9y²+(3x-4y)(3x+4y)=4x²-12xy+9y²+9x²-16y²=13x²-12xy-7y²
解：原式=4x²-12xy+9y²-(16y²-9x²) =4x²-12xy+9y²-16y²+9x² =13x²-12xy-7y²
