（x-y）(x²+xy+y²)；（x+y-1）²；（a+1/2）²

（x-y）(x²+xy+y²)；（x+y-1）²；（a+1/2）²
（x-y）(x²+xy+y²)；（x+y-1）²；（a+1/2）²

（x-y）(x²+xy+y²)；（x+y-1）²；（a+1/2）²
（x-y）(x²+xy+y²)=x^3-y^3
（x+y-1）²
=(x+y)^2-2(x+y)+1
=x^2+2xy+y^2-2x-2y+1
（a+1/2）²
=a^2+a+1/4

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（x-y）(x²+xy+y²)
=x³+x²y+xy²-x²y-xy²-y³
=x³-y³

（x+y-1）²
=(x+y)²-2(x+y)+1
=x²+2xy+y²-2x-2y+1

（a+1/2）²
=a²+2×a×1/2+1/4
=a²+a+1/4