title: Draw a equilateral triangle given the center
body: <p>How do I draw an equilateral triangle given the center as <code>cx</code> and <code>cy</code>
  and the radius of the centroid circle ?</p>
  
  <p>And how do I find if a point is within the triangle or not ?</p>
  
  <p><img src="https://i.stack.imgur.com/r3v4Z.gif" alt="enter image description here"></p>
  
  <p>PS: I am building this for <code>android</code> , but this question is language agnostic. </p>