F.2 Perfect Square questions

1. -1/3(9x-6y)^2
=-1/3[(9x)^2-2(9x)(6y)+(6y)^2]
=-1/3(81x^-108xy+36y^2)
=-27x^2+36xy-12y^2

2. (a^2+b^2)^2
=[(a^2)^2+2(a^2)(b^2)+(b^2)^2
=a^4+4a^2b^2+b^4

3a. Expand (x-2)^2
=(x^2-2(x)(2)+(2)^2
=x^2-4x+4

b. Hence, expand (s+t-2)^2
(s+t-2)^2
=(s+t)^2-4(s+t)+4
=s^2+t^2+2st-4s-4t+4

2010-09-13 18:00:13 補充：
3a. expand (u+3)^2
(u+3)^2
=u^2+2(u)(3)+3^2
=u^2+6u+9

b. hence, expand (2x-y+3)^2
since (2x-y)=u
so(2x-y+3)^2
=(2x-y)^2+6(2x-y)+9
=4x^2+y^2-2xy+12x-6y+9
我係用左hence黎計 如果唔係hence就要拆開黎計

2010-09-13 18:03:28 補充：
如果唔係hence
就(2x-y+3)(2x-y+3)拆黎計
a題已計到(u+3)^2=u^2+6u+9
所以b題就唔洗計就咁代番u=(2x-y)
明唔明?

2010-09-14 18:35:09 補充：
你不是要栘除問題吧.....