[2x的平方-(x+y)(y-x)][3(-x-y)(y-x)+4y的平方]
=【2x²＋x²-y²】【3x²-3y²＋4y²】
=【3x²-y²】【3x²＋y²】
=9x的4次方-y的4次方
=9×(1/3)^4-1^4
=1/9-1
=-8/9