# Quod Erat Demonstrandum

## 2009/01/14

### 16 踢（數學篇）

Filed under: Fun,mathematics,Teaching — johnmayhk @ 12:10 下午

1. 眼睛不能沒眼淚，等式不能沒等號。

2. 愛你的只有一個我，開方的只有一個根。

3. 多愁善感西太后，化簡答案到最後。

4. 先化簡然後爆破，唱兩咀無謂情歌。

5. 恐怖分子，最愛寫恐怖分母。

6. 愛怪物的你，唔好寫 D 怪物給我。

7. 就算計數無圖畫，睇曬 D 字完成它。

8. 全角度愛你，包括銳角、鈍角、直角…

9. Why, why, tell me why，解方程要用因式分解…

10. 青山代數。用零做分母？不如去跳舞。

11. 永遠幾遠？平行線交於無窮遠。

12. 從此世界多了一分鐘？Kai少陣啦！覆卷最少五分鐘o架！

13. 如果世上沒傻瓜，數學成績冇咁差。

14. 考試有渣拿，緊記方妙娜。

15. Mathematics, You Are My Best Friend，你是我杯 hot 茶。

16. 呢篇 note 如果愛？留 cm 啦…

## 5 則迴響 »

1. 1. Don’t think that $x^2 + 2x + 3$ is an equation, it is only an expression! You should write something like “$x^2 + 2x + 3 = 0$“.

2. Once again, $\sqrt{9} \ne \pm 3$, also, $\sqrt{a^2} = |a|$ (not $a$).

3. Don’t write $\frac{2}{12x}$ as the answer, please simplify it as $\frac{1}{6x}$.

4. Just refer to my old post

http://www.hkedcity.net/ihouse_tools/forum/read.phtml?forum_id=27877&current_page=7&i=921576&t=921304&v=f

5. To make denominators the same, students don’t find out the L.C.M., e.g. to simplify $\frac{x + 1}{x^2 - 3x + 2} + \frac{x - 1}{x^2 - 4x + 3}$, they usually write $\frac{(x + 1)(x^2 - 4x + 3)}{(x^2 - 3x + 2)(x^2 - 4x + 3)} + \frac{(x - 1)(x^2 - 3x + 2)}{(x^2 - 3x + 2)(x^2 - 4x + 3)}$, without finding the L.C.M. of the denominators first.

6. students may create some mathematics monster objects to frighten me. (Urm, my ‘heart blood’ is getting lesser…)

7. That is very important, don’t JUST look at figures or diagrams in a mathematics problem. Because some information may not be easily shown in figures. Students should READ ALL WORDS in the questions to find out ALL information required to solve the problem.

8. Don’t forget about the definitions of acute, obtuse and right angle, and there are many other special angles in trigonometry, keep them in mind!

9. It is because factorization is another side of a coin of solving equation. Don’t write something like:

$(x - 1)(x + 2) = (x - 1)(2x + 1) \Rightarrow x + 2 = 2x + 1$, instead, you should use factorization

$(x - 1)(x + 2) = (x - 1)(2x + 1) \Rightarrow (x - 1)[(x + 2) - (2x + 1)] = 0$, factorize first, see?

10. Yes, that is the problem appearing in the wrong method in point 9 above.

11. Want to share something about projective geometry, but, the time…

12. Checking is very important when finishing a test or exam paper, don’t work on the questions until the last minute.

13. Urm, it may not true, mathematics ability is something independent of I.Q.

14. 方妙娜 is not the daughter of Mr. Fong, it should be ‘formula’.

15. But sometimes, mathematics is so cool, she ignores me always.

16. Up to u la.

迴響 由 johnmayhk — 2009/01/14 @ 12:11 下午 | 回應

2. 嘩…用心良苦呀…
最佳授課員非你莫屬啦…
無時無刻都可以教數的呢…

But…我不是很明白statement 2的意思…
開方9為什麼不可以等於-3?

迴響 由 Patrick Wong — 2009/01/14 @ 11:45 下午 | 回應

3. Patrick, please refer to

https://johnmayhk.wordpress.com/2008/09/03/prerequisite-of-f4-algebra/

迴響 由 johnmayhk — 2009/01/14 @ 11:50 下午 | 回應

4. 小記一則：想當年方 sir 弄瓦之喜，
我地班同學幫佢改名，男既叫方程式，女既叫方苗娜。

題外話：平行線不可相交？還看 Euclidean Geometry~ xD

迴響 由 Ricky — 2009/02/18 @ 7:50 下午 | 回應

5. @Ricky

Really good names…

Anyway, let me post a question. Suppose a line L1 overlaps another line L2, can we say they are parallel and intersecting at infinitely many points?

Also, you mean “non-Euclidean Geometry"?

迴響 由 johnmayhk — 2009/02/24 @ 1:51 下午 | 回應