唔識呢幾條數?

1) (2p+3q)^2-(2p+3q)^2
= 4p^2+6pq+9q^2-4p^2-6pq-9q^2
=0

2) (x+y)^2(x+y)^2
= (x^2+2xy+y^2)(x^2+2xy+y^2)
=x^4+4x^3y+6x^2y^2+4xy^3+y^4

3)(x+3)(x-3)(x^2-9)
=(x^2-9)(x^2-9)
=x^2-18x+81

2007-07-31 17:55:33 補充：
Corrected3)(x+3)(x-3)(x^2-9) =(x^2-9)(x^2-9) =x^4-18x^2+81

1) 唔知你有冇打錯題目, 第一個括號同第二個括號既數係一樣...
肯定係 0 喎...
(2p+3q)^2-(2p+3q)^2
= 0

2) (x+y)^2(x+y)^2
= (x^2+2xy+y^2)(x^2+2xy+y^2)
= x^2(x^2+2xy+y^2) + 2xy(x^2+2xy+y^2) + y^2(x^2+2xy+y^2)
= x^4 + 2x^3y + x^2y^2 + 2x^3y + 4x^2y^2 + 2xy^3 + x^2y^2 + 2xy^3 + y^4
= x^4 + (2+2)x^3y + (1+4+1)x^2y^2 + (2+2)xy^3 + y^4
= x^4 + 4x^3y + 6x^2y^2 + 4xy^3 + y^4

3)(x+3)(x-3)(x^2-9)
= (x^2-9)(x^2-9)
= (x^2-9)^2
= x^4 - 18x^2 + 81