數學化簡(要答案+解釋)[急]

1.
(a+b)(a-b)+(b+c)(b-c)+(c-a)(c-a)
=(a^2-b^2)+(b^2-c^2)+(c^2-a^2)
=0

2.(x+y)(x-y)
=x^2-y^2
Use the identity : (a^2-b^2)=(a+b)(a-b)

2009-03-18 15:19:27 補充：
Since (a+b)(a-b)=a^2-ab+ab-b^2=a^2-b^2

1. (a+b)(a-b)+(b+c)(b-c)+(c-a)(c-a)
=(a^2-ab+ab-b^2)+(b^2-bc+bc-c^2)+(c^2-ac-ac+a^2)
=(a^2-b^2)+(b^2-c^2)+(c^2-2ac+a^2)
=a^2+a^2-b^2+b^2-c^2+c^2-2ac
=2(a^2)-2ac
2. (x+y)(x-y)
=x^2-xy+xy-y^2
=x^2-y^2

Although STEVIE-G™ is博士級1級,
But his ans. Wrong!!

海砂之謎 , are you copying STEVIE-G™’s work,
You also wrong!

1.

(a+b)(a-b)+(b+c)(b-c)+(c-a)(c-a)

=(a^2-b^2)+(b^2-c^2)+(c^2-a^2)

=0

2.(x+y)(x-y)

=x^2-y^2

其實好簡單的,,你記住公式依家識做