利用立方和公式因式分解下列各式:
(1) 8X3+27 (2) 27X3+64
(3) a6X3+b3 (4) (X+1)3+(y-1)3
详解:
(1) 8X3 +27
= (2X)3+(3)3
= (2X+3)((2X)2-2X×3+32) (利用立方和公式)
= (2X+3)(4X2-6X+9)
(2) 27X3+64
= (3X)3+(4)3
= (3X+4)((3X)2-3X×4+42) (利用立方和公式)
= (3X+4)(9X2-12X+16)
(3) a6X3+b3
= (a2X)3+(b)3
= (a2X+b)((a2X)2-a2X×b+b2) (利用立方和公式)
= (a2X+b)(a4x2-a2bX+b2)
(4) (X+1)3+(y-1)3
= [(X+1)+(y-1)][(X+1)2-(X+1)(y-1)+(y-1)2] (利用立方和公式)
= (X+y)[(X2+2X+1)-(Xy-X+y-1)+(y2-2y+1)]
= (X+y)[X2+2X+1-Xy+X-y+1+y2-2y+1]
= (X+y)(X2-Xy+y2+3X-3y+3)
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