會考都無C 2017-9-27 02:40:04

其實點解sum of root係a+b , product of root係ab , 教科書似乎一直以嚟都冇解釋過

呢個有咩好解釋

:^(

要解嘅係Sum of roots = -b/a

仲有product of roots係c/a，點

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解?

In expression f(x)=ax^2+bx+c
Since f(alpha)=f(beta)=0, f(x) is divisible by (x-Alpha) and (x-beta)
Therefore, f(x)=ax^2+bx+c=A(x-Alpha)(x-beta)

Comparing leading coefficients and we have A=a
Therefore, f(x)=a(x-alpha)(x-beta)

Result follows from direct expansion and comparing coefficients

做愛用全力 2017-9-27 02:40:43

其實點解sum of root係a+b , product of root係ab , 教科書似乎一直以嚟都冇解釋過

呢個有咩好解釋

:^(

要解嘅係Sum of roots = -b/a

仲有product of roots係c/a，點

:^(

解?

其實唔難明
先let a, b be the roots of quadratic equation
x=a or x=b
x-a=0 or x-b=0
(x-a) (x-b) =0
x^2-(a+b) x+ab=0

會考都無C 2017-9-27 02:50:28 龜sir究竟知唔知自己講緊乜

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會考都無C 2017-9-27 02:55:00 仲有一個
Why radius is perpendicular to tangent at the point of contact

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會考都無C 2017-9-27 02:55:32

Funny questons:
Why volume of sphere (4/3)pie r^3?
Why surface area of sphere is 4pie r^2?
Is it a coincidence that surface area of sphere is the derivative of its volume?

And circles’ circumference and area

會考都無C 2017-9-27 03:00:23

仲有一個
Why radius is perpendicular to tangent at the point of contact

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Just a result from vector calculus that, using dot product in circular motion:
r‧r' = 0

Where r' is the first derivative of r

如果係中學生問你呢個問題呢

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一樣用vector cal拋鳩佢

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Steroid 2017-9-27 07:38:28 精算撚表示背唔到formula

條撚樣想點撚樣呀 2017-9-27 09:36:38 有時d formula 有d 係憑實驗結果 加入去既correction factor既數個d 好難記

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小城大事 2017-9-27 13:14:56

明白啲公式點嚟就唔難記

個問題就係唔明點嚟

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介唔介意具體講多少少?
或者舉啲例子，當中講吓你點樣唔明法?唔明邊一個位?

例如教個啲f(x)=2x+y+10 g(x)=2f(x) (當然會複雜啲)
睇老師做個陣 心諗啲xxyy做乜鳩搬嚟搬去有時唔見咗有時又出現番

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g(x) = 2 (2x+y+10) = 4x+2y+20

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咁都唔明不如去驗腦

好彩你改得快 唔係你要去驗腦

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唔知你係唔小心定係真係錯

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你又係盲撚嚟？我個目的係舉例f(x)=g(x)呢類中學數我唔識呀 使唔使下次copy成個chapter啲數出嚟先得呀

:^(