What you are doing is incredibly dangerous. You can break your site horribly, or have your entire server hacked. With a PHP in content plugin there is nothing stopping an editor from copy pasting a PHP shell in to the content editor and taking full control of your site.
If you have content on a page and want to include custom code, you should use one of the following:
- shortcodes
- custom page templates
- hooks and filters, e.g.
the_content - custom template functions
- custom metaboxes and associated code
There are many alternatives, all well documented and with hundreds of questions asking how to do them from new developers on this site alone. I encourage you to ask!!
You should NEVER use plugins that let you put PHP code inside your posts. If I were to do this, I would face immediate dismissal from my job. I urge you to consider alternatives.