# Tag Info

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### Why does Mathematica get the infinite sum of this representation of the taylor series of $\cos^2(x)$ wrong?

Expanding on the comment by @Goofy and after reading the docs we see that: "ParallelFirstToSucceed" try each method in parallel until one succeeds ...
Accepted

### First argument -h is not a valid variable

h is a local to Series, you cannot use it as a functionargument. Try ...

### Find Generalized Series with Symbolic Variable

With SeriesCoefficient, the order and expansion point can be symbolic. ...

### Find Generalized Series with Symbolic Variable

If I understand correctly what you want the following is your friend ...

### Why does Mathematica get the infinite sum of this representation of the taylor series of $\cos^2(x)$ wrong?

Vs 6 gets the correct result, but Wolfram $\alpha$ decides, too, that \sum_{m,n=0}^\infty \frac{ (-1)^{n+m} x^{2m+2n} }{(2n)!(2m)!} \quad \ne \quad \sum_{m=0}^\infty\left(\sum_{n=0}^\infty \frac{ ...
I'm assuming you want the "formula" for what CoefficientList[Series[f[x], {x, a, n}], x] gives. If you want the term associated with $x^j$, that is the ...