快!幾條中三數!15點

1.p^6-8
2.x^3-y^3+x-y
3.8x^3+y^3-2x-y
4.2m^6-2n^6
5a.因式分解c^2+7c-8(li條我色,唔洗做.THX)
5b.由此,因式分解-x^6-7x^3+8


1. p^6-8
= (p^2)^3 -2^3
= (p^2-2) (p^4+2p^2+4)

2. x^3-y^3+x-y
= (x^3-y^3) + (x-y)
= (x-y) (x^2+xy+y^2) + (x-y)
= (x-y) (x^2+xy+y^2+1)

3. 8x^3+y^3-2x-y
= [(2x)^3+y^3] - (2x+y)
= (2x+y) (4x^2-2xy+y^2) - (2x+y)
= (2x+y) (4x^2-2xy+y^2+1)

4. 吾知點解我用兩個吾同既方法
計到兩個吾同既答案(可能一樣)=o=
方法一:
2m^6-2n^6
= 2 (m^6-n^6)
= 2 [(m^2)^3 - (n^2)^3]
= 2 (m^2-n^2) (m^4+m^2n^2+n^4)
= 2 (m+n) (m-n) (m^4+m^2n^2+n^4)
方法二:
2m^6-2n^6
= 2 (m^6-n^6)
= 2 [(m^3)^2 - (n^3)^2]
= 2 (m^3+n^3) (m^3-n^3)
= 2 (m+n) (m^2-mn-n^2) (m-n) (m^2+mn+n^2)

5(a). c^2+7c-8
= (c+8) (c-1)
5(b). 當(b)入面既'x^3'係'c', 代入(b)
-x^6-7x^3+8
= -(x^6+7x^3-8)
= -[(x^3)^2+7(x^3)-8]
= -(c^2+7c-8)
= -(c+8) (c-1)
= -(x^3+8) (x^3-1)
= (x^3+8) (1-x^3)




希望幫到你喇:)
加油呀中三同學!
比分我喇:D

2010-09-18 21:35:33 補充：
第4題
方法二:
2m^6-2n^6
= 2 (m^6-n^6)
= 2 [(m^3)^2 - (n^3)^2]
= 2 (m^3+n^3) (m^3-n^3)
= 2 (m+n) (m^2-mn+n^2) (m-n) (m^2+mn+n^2)
答案修正!