（1）（2）は変換原稿に含まれていません。 (3) a4+b4+c4−2a2b2−2b2c2−2c2a2=a4−2a2(b2+c2)+(b4−2b2c2+c4)a^{4}+b^{4}+c^{4}-2a^{2}b^{2}-2b^{2}c^{2}-2c^{2}a^{2} = a^{4}-2a^{2}(b^{2}+c^{2})+(b^{4}-2b^{2}c^{2}+c^{4})a4+b4+c4−2a2b2−2b2c2−2c2a2=a4−2a2(b2+c2)+(b4−2b2c2+c4) =a4−2a2(b2+c2)+(b2−c2)2=a4−2a2(b2+c2)+(b+c)2(b−c)2= a^{4}-2a^{2}(b^{2}+c^{2})+(b^{2}-c^{2})^{2} = a^{4}-2a^{2}(b^{2}+c^{2})+(b+c)^{2}(b-c)^{2}=a4−2a2(b2+c2)+(b2−c2)2=a4−2a2(b2+c2)+(b+c)2(b−c)2 ={a+(b+c)}{a−(b+c)}{a+(b−c)}{a−(b−c)}= \{a+(b+c)\}\{a-(b+c)\}\{a+(b-c)\}\{a-(b-c)\}={a+(b+c)}{a−(b+c)}{a+(b−c)}{a−(b−c)} =(a+b+c)(a−b−c)(a+b−c)(a−b+c)= (a+b+c)(a-b-c)(a+b-c)(a-b+c)=(a+b+c)(a−b−c)(a+b−c)(a−b+c)