f2math (因式分解)

81-(x^2-4xy+4y^2)
=81-[x^2-2(x)(2y)+(2y)^2]
=9^2-(x-2y)^2
=[9+(x-2y)][9-(x-2y)]
=(9+x-2y)(9-x+2y)

I am a Maths. tutorial teacher....
so, I sure this answer is correct~
Hope that I can help you~

81-(x^2-4xy+4y^2) [本人會用呢個方法做~比較易明囉~]
=81-(x-2y)^2 [x^2-4xy+4y^2可以分解因式，做(x-2y)^2，(a-b)^2 => a^2 -2ab+b^2]
=9^2 - (x-2y)^2 [之後都可以分解公式，用(a^2-b^2)=> (a+b)(a-b)]
=(9+x-2y)(9-x+2y)
=(x-2y+9)(2y-x+9)

81-(x^2-4xy+4y^2)
=81-(x^2-4(x)(y)+4y^2) [呢度都仲correct]
=9^2-(x+4Y)62 [呢度就唔太明點解要抽個62 出來囉~因為你就算將個62 乘返入去，都同原來有分別~所以呢度已經開始做錯左囉~~]
=[9+(x+4y)][9-(x-4y)]
=(9+x+4y)(9-x-4y)

tom777g你錯了
A²-B² =(A+B)(A-B)≠(A-B)²

2007-01-01 17:33:05 補充：
條數應該係先解(x² -4xy+4y² ) => (x-2y)² 然後用番上面個條式A²-B² =(A+B)(A-B)9²-(x-2y)² =>(9+x-2y)(9-x+2y)應該係咁啦希望幫到你~

81-(x^2-4xy+4y^2)

=81-(x-2y)^2

=9^2-(x-2y)^2

=(9-x+2y)^2

應該係咁.......

81-(x^2-4xy+4y^2)
=81-(x^2-4(x)(y)+4y^2)
=9^2-(x-2Y)^2
=[9+(x-4y)][9-(x-4y)]
=(9+x-4y)(9-x+4y)

2007-01-01 17:16:52 補充：
上面打錯, 呢個先岩81-(x^2-4xy 4y^2)=81-(x^2-4(x)(y) 4y^2)=9^2-(x-2Y)^2=[9 (x-2y)][9-(x-2y)]=(9 x-2y)(9-x 2y)

2007-01-01 17:18:58 補充：
上面唔知做咩冇+號,應如下81-(x^2-4xy+4y^2)=81-(x^2-4(x)(y)+4y^2)=9^2-(x-2Y)^2=[9+(x-2y)][9-(x-2y)]=(9+x-2y)(9-x 2y)

2007-01-01 17:20:22 補充：
上面唔知做咩冇+號,應如下81-(x^2-4xy+4y^2)=81-(x^2-4(x)(y)+4y^2)=9^2-(x-2y)^2=[9+(x-2y)][9-(x-2y)]=(9+x-2y)(9-x+2y)