Form3 maths急問,聽日test牙!!!!岩哂10000好友元 [復制鏈接]

我黎遲左呀?

我都有諗log先
不過見你地d方法咁直接喎

數學有時奇妙在可以用唔同方法計到
殊途同歸
答案始終一天找到了

引用第42樓卡卡....於2006-10-26 23:05發表的“”:
log [表情]
2^x X 2+2^x/2=203
2^x(2+1/2)=203
2^x=203/(2+1/2)
.......

係bo
禁錯機
我頭先都用log
不過F.3教左未?

F.3應該教左
log 10
log 其他就可能未

question2

If x+ 1/x = 5, find x^2/x^4+x^2+1

係咪 x^2/(x^4+x^2+1)?

仲有邊條未做好?

等我快快手ko完佢, 仲要溫通頂.....

引用第49樓ballballfull於2006-10-26 23:59發表的“”:
question2
If x+ 1/x = 5, find x^2/x^4+x^2+1
係咪 x^2/(x^4+x^2+1)?

Hint: divide both denominator and numericator by x^2

then get 1/ (x^2+1+x^-2)

then use result of Q1

Ans = 1/24

a )Expand (x+x^-1)^2
(x+x^-1)^2
=x^2+2+x^-2

注: (a+b)^2 = a^2 + 2ab + b^2

b )given that x   + x^-1   = 5 ,determine x^2 + x^-2
x2+x^-2
= (x+x^-1)^2-2 (By part a)
= 5^2-2
=23

question2

If x+ 1/x = 5, find x^2/x^4+x^2+1
[注:我當係x^2/(x^4+x^2+1)]

x^2/(x^4+x^2+1)
= [(x^4+x^2+1)/x^2 ]^-1
=[x^2+1+x^-2]^-1
=1/(1+23) (By part 1b)
=1/24

question3

2^2x+1 +   2^2x-1   =   203
find x

2 (2^2X) + 0.5 (2^2X) = 203
2.5 (2^2X) = 203
2^2X = 81.2
2x log2 = log 81.2
x= log81.2 / (2log2)
x=3.1717 (corr. to 4 dp.)

question4

2^x+3   +2^x   = 9/16

find x

2^x+3 + 2^x = 9/16
8 (2^X) + 2^x = 9/16
9 (2^x) = 9/16
2^x = 1/16
X = -4

引用第52樓ballballfull於2006-10-27 00:20發表的“”:
a )Expand (x+x^-1)^2
(x+x^-1)^2
=x^2+2+x^-2
b )given that x   + x^-1   = 5 ,determine x^2 + x^-2
.......

all are correct

我估可能係

2^2x+1 +   2^2x-1   = 320

X=3.5

=================================

岩哂10000好友元

"豆寧"都冇...
早知唔計

haha 臨急抱佛腳  

十點先黎問

引用第50樓kylau於2006-10-27 00:01發表的“”:
仲有邊條未做好?
等我快快手ko完佢, 仲要溫通頂.....

kylau你加下讀跟咩程度,次次到親你個版都見你解哂其他好友既難題,佩服

第二題有問題


好耐未掂過呢D數lu

引用第56樓卡卡....於2006-10-27 17:29發表的“”:
kylau你加下讀跟咩程度,次次到親你個版都見你解哂其他好友既難題,佩服 [表情]

起馬大學啦

引用第58樓eric_ah4於2006-10-27 18:49發表的“”:
起馬大學啦 [表情]

HKU 架