Let $f(x)$ positive-homogeneous convex function ($f(cx)=cf(x)$ for all $c \geq 0$)
$A := \{ x \in \mathbb{R}^n : f(x)\leq 1\}$.
$A^{\circ}$ is polar set for $A$.
How to prove that $A^{\circ} = conv(\partial f(0) \cup \{0\})$?
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I see that constraint $f(x)\leq 1$ actually can lead to polar set but I have no idea how to prove it.