equation既問題

小霞的fans

近來開post開得好密><希望大家原諒~

suppose a and b are the roots of the equation 10x^2-20x+1 = 0
without solving the above equation , find the value of

a)4^a x 4^b ,

b)loga + logb

唔solve條式點搵a 同 b既值呢,,thx~

sapphire

For this kind of question, it is not necessary to solve a and b.

a + b = 20/10 = 2
ab = 1/10

(a) 4^a * 4^b = 4^(a + b)
(b) log(a) + log(b) = log(ab)
and do the calculation......

Actually, when you see this kind of question (without finding the roots), you may think about the sum of root and the product of root.

小霞的fans

For this kind of question, it is not necessary to solve a and b.

a + b = 20/10 = 2
ab = 1/10

(a) 4^a * 4^b = 4^(a + b)
(b) log(a) + log(b) = log(ab)
and do the calculation......

Actually,  ...
sapphire 發表於 16/2/2010 08:04 PM

                               
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點解a + b = 20/10 = 2 既!?
糟糕,,我咁基本都唔識 .....

ice

點解a + b = 20/10 = 2 既!?
糟糕,,我咁基本都唔識 .....
小霞的fans 發表於 17/2/2010 04:23 PM

                               
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因為sum of roots = -b/a (ax^2+bx+c)

小霞的fans

因為sum of roots = -b/a (ax^2+bx+c)
IceDragon 發表於 16/2/2010 08:38 PM

                               
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@[]@而家先知有呢條式,,上堂冇用過呢條式
仲有其他式的嗎?

unlock-YM

@[]@而家先知有呢條式,,上堂冇用過呢條式
仲有其他式的嗎?
小霞的fans 發表於 17/2/2010 05:15 PM

                               
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A Maths的... 基本上冇讀過就唔會識。(唔知現時CE Maths syllabus有冇)

ice

@[]@而家先知有呢條式,,上堂冇用過呢條式
仲有其他式的嗎?
小霞的fans 發表於 17/2/2010 05:15 PM

                               
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仲有product of roots = c/a (這個你應該懂了)
delta = b^2-4ac
delta>0 = 2 distinct real roots
       =0 = 2 equal real roots
       <0 = unreal roots
大概就這些了

Luna

A Maths的... 基本上冇讀過就唔會識。(唔知現時CE Maths syllabus有冇)
unlock-YM 發表於 17/2/2010 05:19 PM

                               
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334學生表示中四上學期教了
p.s.是core syllabus

unlock-YM

8# Luna

334? 咁我完全唔會懷疑... 聽聞更有complex number。

Sorry 版主，好似click錯報告，但係搵唔到點delete已發送pm，唔多熟呢個Discuz!版本。

hk56740

9# unlock-YM
冇錯呀,334 compulsory maths的確要讀complex no.同sum and product of root,仲有heron's formula