Iframe Tag just adds another window on your Webpage and due to which whenever a browser loads a page with an iframe it loads the original Page and Iframe as a separate 2 different pages. So in some cases Iframe is not-supported and thus, displays an Error.
Sigma is a Greek letter that corresponds somewhat to our letter S and thus sigma is often used to stand for some concept that starts with S. There is an upper case (capital) sigma and a lower case (small) sigma. They are and. is most ofter used to indicate a sum.
The first and most common formula related to the sigma symbol is the summation notation using the upper case sigma. The less common formula is the one for standard deviation used in statistics. This second formula uses the lower case sigma. To unlock this lesson you must be a Study.com Member.