title: Is std::sqrt the same as sqrt in C++
body: <p>I'm very new to C++, I have this piece of code, the code looks like this:</p>
  
  <pre><code>D = (sum_B / double(E))*std::sqrt(E)
  </code></pre>
  
  <p>Can someone interpret it into a math formula or something easy to understand, I'm not sure what is this <code>std::sqrt</code> , wondering if it is the same with my formula:</p>
  
  <pre><code>A = sum(B*C)/sum(B)
  D = A * sqrt(E)
  </code></pre>
  
  <p>(A/B/C/D/E represent different columns in my dataset)</p>