Definition:Half-Range Fourier Cosine Series/Formulation 1

Definition
Let $\map f x$ be a real function defined on the interval $\openint 0 \lambda$.

Then the  half-range Fourier cosine series of $\map f x$ over $\openint 0 \lambda$ is the series:


 * $\map f x \sim \dfrac {a_0} 2 + \displaystyle \sum_{n \mathop = 1}^\infty a_n \cos \frac {n \pi x} \lambda$

where for all $n \in \Z_{\ge 0}$:
 * $a_n = \displaystyle \frac 2 \lambda \int_0^\lambda \map f x \cos \frac {n \pi x} \lambda \rd x$