## Need help finding the function of an expansion

1. The problem statement, all variables and given/known data

can anybody help with finding the function whos expansion is this -(5/16)x^7+(21/16)x^5-(35/16)x^3+(35/16)x

I looks like a function of sin(X) but I just cant nail down what it is.

2. Relevant equations

3. The attempt at a solution

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 Quote by delta59 1. The problem statement, all variables and given/known data can anybody help with finding the function whos expansion is this -(5/16)x^7+(21/16)x^5-(35/16)x^3+(35/16)x I looks like a function of sin(X) but I just cant nail down what it is.
Have you looked at the graph?

It doesn't look like a sine curve to me, more like a polynomial of some sort, heh heh.

 Recognitions: Gold Member Science Advisor Staff Emeritus What do you mean by "expansion"? Since you have powers of x I would have thought "Taylor's series" but the Taylor's series of any thing other than a polynomial is an infinite series. Any finite "expansion" in powers of x is just the polynomial it looks like. And if you mean this to be the first seven terms of a power series, you will have to tell us what the general coefficient is.