title: Scale an equation to fit exact page width
body: <p>I have an equation that is only a tiny bit too wide for one line. I'd really like to avoid having the equation number on the next line. How do you achieve this? Currently I'm using <code>\small</code>, but this is overkill.</p>
  
  <p><strong>Please note.</strong> I have tried <code>scalebox</code> and <code>fittowidth</code> but get errors about missing <code>\endgroup</code>. I have also used <code>\!</code> to its full extent. I am hoping for a solution that will allow me to scale the proper one-line equation to the width of the page.</p>
  
  <p>Here is an example (not my actual equation):
  <a href="https://i.stack.imgur.com/CZUHD.png" rel="noreferrer"><img src="https://i.stack.imgur.com/CZUHD.png" alt="Long equation"></a></p>