A. Maths. Test..........!!!!

細薯

today after school ...........i had an A. Maths. Test..........
i have only revise for 1 minutes......
then.......
i wrong/don't know how to do quite many questions.........

this is the first question~

total full marks:43

1. solve the equation

|    2     |
|-----------| = x                                    (4%)
|  x+1    |

fish

smallpotato226  在 2004-10-18 05:58 PM 發表:

today after school ...........i had an A. Maths. Test..........
i have only revise for 1 minutes......
then.......
i wrong/don't know how to do quite many questions.........

this is the first ...

是    2/(x+1) =x  嗎?

PS我唔係A.Maths 生XD

oscar

When x>0,
|   2   |
|--------|=x
| x+1  |

   |2|
----------=x
  |x+1|

   2
--------=x
x+1

2=x^2+x
x^2+x-2=0
x=1,-2 (rejected)

When x<0,
|   2   |
|--------|=x
| x+1  |

   |2|
----------=x
  |x+1|

   2
--------=x
  -x-1

2=-x^2-x
-x^2-x-2=0
x^2+x+2=0
Since the solution of x here is >0, the solutions are rejected.

So, the solution is x=1

[ Last edited by oscar on 2004-10-18 at 06:39 PM ]

Echo21

我班今都有A.Math的test
我只懂Sum of MI......

oscar

Echo21  在 2004-10-18 18:57 發表:

我班今都有A.Math的test
我只懂Sum of MI......

乜唔係應該教左Quadratic Equations & Functions先嫁咩...

Echo21

oscar  在 2004-10-18 19:11 發表:

乜唔係應該教左Quadratic Equations & Functions先嫁咩...

MI→Binomial Theo.→Quadratic Equations & Functions

SusanCrystal

做左2題binomial咋…
都唔知有冇10分....(100分滿分)

細薯

回oscar:
this question 我識ar~~(第一題較容易)

fish  在 2004-10-18 06:07 PM 發表:

是    2/(x+1) =x  嗎?

PS我唔係A.Maths 生XD

唔係A.Maths 生難怪
下面的東東叫absolute value~

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[ Last edited by smallpotato226 on 2004-10-18 at 08:00 PM ]

Echo21

SusanCrystal  在 2004-10-18 19:38 發表:

做左2題binomial咋…
都唔知有冇10分....(100分滿分)

剛才才發現
原來沒有收份卷......
我想我有40分......

抹茶可樂

|    2    |
|---------| = x
|  x+1    |

|x+1|=2/x
x+1=±2/x  <+必殺step，分case比較煩，無必要唔好用
x^2+x+2=0 OR x^2+x-2=0
Δ=1-8=-7  OR  (x+1)(x-1)=0
No Real   OR  x=1 OR x=-1(rej.) <When x=-1,LHS becomes 2/0>

So x=1

逢係所有除以x的數都會有人中招，
他們並沒有留意答案會不會變成0

[ Last edited by 落雷 on 2004-10-18 at 08:53 PM ]