title: How do I use std::num::sqrt to compute the square root of a number?
body: <p>I want to take the square root of a number.</p>
  
  <p>I looked at the documentation <a href="http://doc.rust-lang.org/0.10/std/num/fn.sqrt.html" rel="noreferrer">here</a>, and wrote <code>use std::num;</code> at the top of my program which I thought would have allowed me to <code>sqrt</code>. This doesn't work though, so what do I need to do to actually use <code>std::num::sqrt</code>?</p>
  
  <pre><code>let upperLimit: i64 = sqrt(num as f64) + 1; //doesnt work
  </code></pre>
  
  <p>I'm very new to Rust coming from c++, so I really don't understand that real use of <code>use</code>.</p>