Add missing minus sign in equation, closes #192

6 jobs for fix_eq in 11 minutes and 7 seconds (queued for 1 second)
Status Name Job ID Coverage
  Execute
passed execute_ipynbs #14058

00:08:07

passed mirror to github #14059

00:00:39

 
  Build
passed edx archive #14060

00:01:21

passed ocw website #14062

00:01:15

passed pelican website #14061

00:01:56

 
  Deploy
passed upload test website #14063

00:01:04