查看完整版本: Binomial expansion question and its application
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190303458 發表於 2013-1-12 01:18 PM

Binomial expansion question and its application

Expand (1-3x)^(-1/2) up to the term x^3.
Hence find (12)^(1/2) to the 3 decimal places.


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chongwaikei 發表於 2013-1-12 10:50 PM

本帖最後由 chongwaikei 於 2013-1-13 05:44 PM 編輯

http://latex.codecogs.com/gif.latex?\begin{align*}%20(1-3x)^{-\frac{1}{2}}&=\sum_{n\geq0}\binom{-\frac{1}{2}}{n}(-3x)^n\\&=1+\frac{3x}{2}+\frac{27x^2}{8}+\frac{135x^3}{16}+O(x^4)\end{align*}


you can finish the 2nd part now

190303458 發表於 2013-1-14 03:06 PM

I just can't solve the 2nd part. Would you please tell me how to solve?

chongwaikei 發表於 2013-1-14 04:16 PM

本帖最後由 chongwaikei 於 2013-1-14 04:31 PM 編輯

190303458 發表於 2013-1-14 03:06 PM static/image/common/back.gif
I just can't solve the 2nd part. Would you please tell me how to solve?
http://latex.codecogs.com/gif.latex?\\$That%20is%20quite%20easy%20,%20$\frac{1}{\sqrt{1-3x}}=\sqrt{12}\\\\%20$find%20$x$%20and%20sub%20into%20the%20part%20a)%20$\\\\
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chongwaikei 發表於 2013-1-14 04:49 PM

本帖最後由 chongwaikei 於 2013-1-14 04:54 PM 編輯

I tested the series of the answer in part a).

The series doesn't converge fastly.

If you want to get the answer √12 = 3.464....

maybe you need at least 15 terms of the series


or your teacher only wants the answer of the first 3 terms
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