(2x-3y)²+(2x+3y)²=4x²-12xy+9y²+4x²+12xy+9y²=8x²+18y² (2x-3y)²-(2x+3y)²=[(2x-3y)+(2x+3y)][(2x-3y)-(2x+3y)]=(4x)(-6y)=24xy
=4x^2+9y^2-12xy+4x^2+9y^2+12xy=8x^2+18y^2
原式=8x²+18y²
