english & maths da qust

你好～～～

有關 My hobby 的問題，可以參考以下這則知識＋的︰

http://hk.knowledge.yahoo.com/question/question?qid=7009081501490

1) a^2 + 2a - 25

上面這道題目應該不是 - 25，是 - 35 才對吧？

a^2 + 2a - 35

= (a - 5)(a + 7)

Hence factorize -4a^2 - 8a + 140.

-4a^2 - 8a + 140

= -4(a^2 + 2a - 35)

= -4(a - 5)(a + 7)

2) b^2 - 10b + 21

= (b - 3)(b - 7)

Hence factorize (m + 1)^2 - 10(m + 1) + 21.

(m + 1)^2 - 10(m + 1) + 21

= (m + 1 - 3)(m + 1 - 7)

= (m - 2)(m - 6)

3) c^2 - 8c - 20

= (c + 2)(c - 10)

Hence factorize y^2(y - 3)^2 - 8y(y - 3) - 20.

y^2(y - 3)^2 - 8y(y - 3) - 20

= [y(y - 3)]^2 - 8[y(y - 3)] - 20

Let y(y - 3) be z.

= z^2 - 8z - 20

= (z + 2)(z - 10)

= [y(y - 3) + 2][y(y - 3) - 10]

= (y^2 - 3y + 2)(y^2 - 3y - 10)

= (y - 1)(y - 2)(y - 5)(y + 2)

希望可以幫到你～～～～～

For Maths
Factorize b^2-10b+21:
(b-7)(b-3)

Factorize c^2-8c-20:
(c-10)(c+2)

2011-10-01 22:09:10 補充：
希望能幫幫你！

2011-10-01 22:14:23 補充：
For writing, I don't know your hobby so you must do it yourself, plus, 100 words are easy.

2011-10-01 22:25:04 補充：
Hence factorize -4a^2-8a+140:
-4(a^2+2a-35)
=-4(a+7)(a-5)