| ■No421に返信(nobuさんの記事) xy(x^2−y^2)+yz(y^2−z^2)+zx(z^2−x^2) ●(x−y)でくくることを考える =xy(x^2−y^2)+(y^3)z−y(z^3)+(z^3)x−z(x^3) =xy(x^2−y^2)−z(x^3−y^3)+z^3(x−y) =xy(x+y)(x−y)−z(x−y)(x^2+xy+y^2)+z^3(x−y) =(x−y){xy(x+y)−z(x^2+xy+y^2)+z^3} =(x−y){(x^2)y+x(y^2)−z(x^2)−xyz−(y^2)z+z^3} ●(y−z)でくくることを考える =(x−y)[(y−z)(x^2)+xy(y−z)−z{(y^2)−(z^2)}] =(x−y)[(y−z)(x^2)+xy(y−z)−z(y+z)(y−z)] =(x−y)(y−z){(x^2)+xy−z(y+z)} =(x−y)(y−z){(x^2)+xy−yz−(z^2)} ●(x−z)でくくることを考える =(x−y)(y−z){(x^2)−(z^2)+xy−yz} =(x−y)(y−z){(x+z)(x−z)+y(x−z)} =(x−y)(y−z)(x−z){(x+z)+y} =(x−y)(y−z)(x−z)(x+y+z) ●(x−z)=−(z−x)を利用し形を整える =−(x−y)(y−z)(z−x)(x+y+z)
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