If you want to hide the quick launch on a SharePoint page or web part page in 2013 you could of cause use CSS scripts as in 2010. But as a new thing in 2013 the user have the possibility to click on full screen mode. so why not load your page in this mode and then the user can choose to exit the mode if he prefers. Add a content editor webpart to your page and click on Edit HTML from the ribbon. Add the following code: <script type="text/javascript"> window.onload = function() { SetFullScreenMode(true); } </script>
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