Need help finding the function of an expansion

[delta59]

Homework Statement

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 can't nail down what it is.

Homework Equations

The Attempt at a Solution

 

[LCKurtz]

Homework Statement

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 can't 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.

 

[HallsofIvy]

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.