F.4 A.Math 2題 3天 20分

2008-11-15 5:15 am

1.If x-1/x=3,find the value of

(a) x^3-1/x^3

(b) x^4+1/x^4

(c) x^5-1/x^5

2.If y^2+1/y^2=4,find the value of

(a) y+1/y

(b) y^4+1/y^4

(c) y^6+1/y^6

更新1:

想回應第2個- - 我想講x-1/x=3 個x係唔調得去右邊因為有個x- 如果可以我就唔駛特登問啦唔通我讀A.MATH托的- -?

更新2:

回第1位,我唔明你1(A)第1步點黎- -

更新3:

回第1位,2(A)第2步個減2點黎@@? 1(A)第1步右手邊唔明!!BUT答案岩,1(B)答案好似錯

更新4:

再回第1位,2(A)你睇錯題= =

回答 (2)

用戶7639

2008-11-15 5:53 am

✔ 最佳答案

As follow AS~~~

圖片參考：http://img171.imageshack.us/img171/6182/screenhunter01nov142156cg5.gif

2008-11-15 07:41:08 補充：
1(b)
x^4 +1/x^4
=(x-1/x)^4 +4x^2-6+4/x^2
=(x-1/x)^4+4(x^2+1/x^2)-6
=(x-1/x)^4+4(x^2-2+1/x^2+2)-6
=(x-1/x^4)+4(x-1/x)^2 +8-6
=3^4 +4(3)^2+2
=119
http://cg-love.com/s9/b6deame.gif

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少坪

2008-11-15 5:55 am

其實呢里幾條數都唔系好難者...以下既解答希望你可以細心參詳一下喇
第一題:
首先你需要搵出個X既值之後就計到嫁喇
x-1=3x
2x=-1
x=-1/2
而家可以代返個值系D式度喇!
(a)(-1/2)^2/(-1/2)3
=1/4 除 -1/8
=1/4 乘 -8/1
= -2

(b)(-1/2)^4+1/(-1/2)^4
=1/16+16/1
=1/16+256/16
=257/16

(c)(-1/2)^5-1 除 (-1/2)^5
=(-1/2)^4 除 (-1/2)^5
=2

2.
y=0(rejected) or y = 4
(a)5/4
(b)4
(c)4

唔知有無錯呢?有錯請大家多多指教呀!

參考: 自己

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