(x+y)²+6(x+y)+9 a²－2a(b+c)+(b+c)² 4xy－4x²y－y³ －a＋2(x+y)²+6(x+y)+9a²－2a(b+c)+(b+c)²4xy－4x²y－y³－a＋2a²－a³

(x+y)²+6(x+y)+9 a²－2a(b+c)+(b+c)² 4xy－4x²y－y³ －a＋2
(x+y)²+6(x+y)+9
a²－2a(b+c)+(b+c)²
4xy－4x²y－y³
－a＋2a²－a³

(x+y)²+6(x+y)+9=(x+y+3)²
a²－2a(b+c)+(b+c)²=[a-(b+c)]²=(a-b-c)²
4xy－4x²y－y³=-y(4x²-4xy+y²)=-y(2x-y)²
－a＋2a²－a³=-a(1-2a+a²)-a(1-a)²

因式分解？