title: How to draw Circle using Turtle in Python 3
body: <p>This is the code that I have already, but it is saying I need to define 'polygon' which I know I need to, but not exactly sure how and different ways that I have been trying just keeps giving me errors. </p>
  
  <pre><code>import turtle
  import math
  
  apple=turtle.Turtle()
  
  def draw_circle(t, r):
      circumference = 2 * math.pi * r
      n = 50
      length = circumference / n
      polygon(t, n, length)
  
  draw_circle(apple, 15)
  
  turtle.exitonclick()
  </code></pre>