# Euclidean space

A space the properties of which are described by the axioms of Euclidean geometry. In a more general sense, a Euclidean space is a finite-dimensional real vector space $\mathbb{R}^n$ with an inner product $(x,y)$, $x,y\in\mathbb{R}^n$, which in a suitably chosen (Cartesian) coordinate system $x=(x_1,\ldots,x_n)$ and $y=(y_1,\dots,y_n)$ is given by the formula $$(x,y)=\sum_{i=1}^{n}x_i y_i.$$

Sometimes the phrase "Euclidean space" stands for the case $n=3$, as opposed to the case $n=2$ "Euclidean plane", see [1], Chapts. 8, 9.