title: what is the type of PI, cos in Ruby
body: <p>I want to ask about the type of PI and cos with Ruby.
  What is the convention to write these types?</p>
  
  <p>Can I write like: <code>Math::sin</code>, <code>Math::PI</code> or <code>Math.sin</code>, <code>Math.PI</code>?</p>