試分解下列各式:
<1> x12 + x9 + x6 + x3 + 1 (大陸試題)
<2> (a + b)7- a7 - b7 (IMO 變形)
<3> x4 + y4 + (x + y)4 (常考考題)
<4> (a+b)(b+c)(c+a)+abc (應用公式)
<5> x3 + y3 - 6xy + 8
<6> a4 + b4 + c4 - 2a2b2 - 2b2c2 - 2c2a2