# How to show a set is convex

Looking for a hint on show to show convexity in a set....

Let $f\colon \mathbb{R}^n \rightarrow \mathbb{R}$ be a convex function and let $c$ be some constant.

Show that the set $s=\{x \in \mathbb{R}^n \mid f(x) \le c \}$ is convex.

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Sorry for the editing confusion. I realise I don't know how latex works here. –  Rasmus Sep 30 '10 at 18:08