subexpressions (OT: math)

[Peter Otten]

Wildemar Wildenburger wrote:

> Peter Otten wrote:
>> With y = x^2 = 1/3 pi^2 - 4(cos x - cos(2x)/2^2 + cos(3x)/3^2 - ...)
>>
>> area is dimensionless, too, I suppose.
>>   
> 
> Ehr, ... maybe this is obvious, but I don't see it: Please explain the
> second equality sign.

I know not much more about Fourier series than that they do exist, so let me
refer you to

http://en.wikipedia.org/wiki/Fourier_series

for a general explanation, and to

http://www.exampleproblems.com/wiki/index.php/FS6

for the series given above.

Peter