MATHS (20 FUN)

[(m+n)(m-n)]^2
= (m^2 - n^2)^2 <-----因為a^2 - b^2 = (a+b)(a-b)
= m^4 - 2m^2n^2 + n^4

2007-10-06 12:54:48 補充：
老實說, 應列的式都列了, 我看不出有寫更多步驟的需要...只是運用了兩個恆等式:1. a^2 - b^2 = (a b)(a-b)2. (a - b)^2 = a^2 - 2ab b^2

2007-10-06 12:56:16 補充：
補充入面應該係:2. (a - b)^2 = a^2 - 2ab + b^2 先o岩, 唔知點解頭先出少左個 "+"

2007-10-06 12:59:13 補充：
嘩...原來連第1條恆等o既 "+" 都冇埋...個system搞乜鬼 =_=1. a^2 - b^2 = (a+b)(a-b)

[(m+n)(m-n)]^2
=[m^2-n^2]^2
=[m^2-n^2] [m^2-n^2]
=m^4-m^2n^2+m^2n^2+n^4
=m^4+n^4
=mn^4 <---------Anwser

[(m+n)(m-n)]^2

=[m^2-mn+mn-n^2]^2

=[m^2-n^2]^2

=[m^2-n^2] * [m^2-n^2]

=m^4 - (m^2)(n^2) - (m^2)(n^2) + n^4

=m^4 - 2(m^2)(n^2) + n^4 ,,