Welcome to MSE
This is a comment Arturo used to add to questions of relatively new users:
Welcome to math.SE: since you are new, I wanted to let you know a few things about the site. Titles should be informative. In order to get the best possible answers, it is helpful if you say in what context you encountered the problem, and what your thoughts on it are; this will prevent people from telling you things you already know, and help them give their answers at the right level. If this is homework, please add the homework tag; people will still help, so don't worry. Also, many find the use of imperative ( "Use") to be rude when asking for help; please consider rewriting your post.
Welcome to math.SE: since you are new, I wanted to let you know a few things about the site. Titles should be informative. In order to get the best possible answers, it is helpful if you say in what context you encountered the problem, and what your thoughts on it are; this will prevent people from telling you things you already know, and help them give their answers at the right level. If this is homework, please add the [tag:homework] tag; people will still help, so don't worry. Also, many find the use of imperative ( "Use") to be rude when asking for help; please consider rewriting your post.