（x＋y﹚的四次方＋2﹙x²－y²﹚²＋﹙x－y﹚的四次方
=（x＋y﹚的四次方＋2﹙x+y)²(x-y﹚²＋﹙x－y﹚的四次方
=[(x+y)²+(x-y)²]²
=(x²+2xy+y²+x²-2xy+y²)²
=(2x²+2y²)²
-=4(x²+y²)²