# Parseval's equality and theorem?

1. Sep 21, 2009

### car202

It's kind of dumb question..
But, I just wanted to make sure.
Are Parseval's equality and Parseval's theorem same thing? (In terms of Fourier series)
i.e. do both mean $$\frac{1}{L}\int_c^{c+2L}|f(x)|^{2}dx = \frac{a_0^2}{2}+\sum_{n=1}^{\infty}[|a_n|^{2}+|b_n|^{2}]$$

2. Sep 22, 2009

### HallsofIvy

Staff Emeritus
Basically, yes. Parceval's equality is the equality you give. Parseval's thereom is the statement that that equality holds, under given hypotheses, of course. Perhaps the crucial difference is the hypotheses. Parceval's equality doesn't make sense without specifying what "f", "an", "bn", etc. are.