The URL https://m.facebook.com/?_rdr is a legitimate, standard mechanism used by Facebook to detect devices and redirect users to the mobile-optimized version of the site. The "_rdr" parameter signifies a redirection, often used for device detection, URL normalization, or secure login processes. For a discussion on this topic, visit Reddit www.reddit.com/r/facebook/comments/2y43u9/wwwfacebookcom_rdr/.

: Post when your audience is most active. Use Facebook Insights to determine the best times to post.

If your content involves mathematics, such as explaining a concept or solving a problem, use $$ syntax for equations: "The Pythagorean theorem is given by $$a^2 + b^2 = c^2$$, where (c) is the length of the hypotenuse of a right-angled triangle."