1a..因式分解 (x3次方) + (27)---->呢條我識...因為2條連住..唔知有冇關係..so打埋.
1b..由此,因式分解 (x 3次方) - 7x + 6----->呢條我計左好耐都唔識做呀.....
唔該大家幫下我啦......
唔該哂!!!!thzzzz.....
急!!!!!!!F.3數學題.....唔該大家幫幫手呀!!!!!
2007-10-27 7:53 am
回答 (2)
2007-10-27 8:00 am
✔ 最佳答案
1a.(x^3) + 27
= (x^3) + (3^3)
= (x + 3)(x^2 - 3x + 9)
1b.
(x^3) - 7x + 6
= (x^3) - 7x + 27 - 21
= (x^3) + 27 -7x - 21
= (x + 3)(x^2 - 3x + 9) - 7 (x + 3)
= (x + 3)(x^2 - 3x + 9 - 7)
= (x + 3)(x^2 - 3x + 2)
= (x + 3)(x - 2)(x - 1)
有錯請指正!
參考: My Maths knowledge
2007-10-27 8:06 am
1a)x^3+27
=x^3+3^3
=(x+3)(x^2+3x+9)
1b)f(x)=x^3-7x+6
f(-3)=(-3)^3-7(-3)+6
=0
所以(x+3)是因式。
f(1)=1^3-7(1)+6
=0
所以(x-1)是因式。
f(2)=2^3-7(2)+6
=8-14+6
=0
所以(x-2)是因式。
x^3-7x+6
=(x+3)(x-1)(x-2)
=x^3+3^3
=(x+3)(x^2+3x+9)
1b)f(x)=x^3-7x+6
f(-3)=(-3)^3-7(-3)+6
=0
所以(x+3)是因式。
f(1)=1^3-7(1)+6
=0
所以(x-1)是因式。
f(2)=2^3-7(2)+6
=8-14+6
=0
所以(x-2)是因式。
x^3-7x+6
=(x+3)(x-1)(x-2)
收錄日期: 2021-04-13 14:11:18
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