Now, the last equality is true if , so now just substitute here , get a
quadratic inequality in and check that iit is always true...
Hmmm...if you're a beginner the above may be a little hard (if you're in high school you shoud be able to do it, though), so perhaps there's
an easier way to do it WITHOUT the use of derivatives.
Also remember than in english, just as in spanish, german, russian, italian, etc., when you begin a sentence after a
period you must use capital letters.