# Question regarding Binomial expansion.

1. Jan 1, 2005

### Sanosuke Sagara

I have my question and my problem in the attachment that followed.

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2. Jan 1, 2005

### quasar987

By "fourth root of 19/21", they mean the quantity $(19/21)^{1/4}$.

Like in your other question, you would like to find the x meeting the condition "x^3 is ignorable" and such that

$$\frac{1-x}{1+x}=\frac{19}{21}$$

You will find that x easily by solving this last equation for x.

Then, with n=1/4, your polynomial formula gives you the wished approximation.

3. Jan 1, 2005

### Sanosuke Sagara

Thanks for your help.I think I now can understand with what the question want.