Beautiful theorem

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Let $t$ is a tangent to the circle $k$ with radii $R$. $P$ is a random point on $k$. $M$ is the feet of the perpendicular from $P$ to $t$ and $N$ is the intersection point of this perpendicular with $k$. Prove that $MN+MP=2R$.

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It is too easy. Don't loose your time.