title: How to know if a point is locate at outer circle?
body: <p>Having a circle with the centre (xc,yc) with the radius r how to know whether a point (xp,yp) is locate at the outer circle which following in the picture below.</p>
  
  <p><a href="https://i.stack.imgur.com/Xz6ky.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Xz6ky.png" alt="enter image description here"></a></p>