# easy function question ?

• May 9th 2009, 05:34 AM
djmccabie
easy function question ?
given that f(x) = e^x - x - 1, show that f is an increasing function for x>0

OK i can see that this statement is true... but i just don't know how to write it on paper...
• May 9th 2009, 05:55 AM
bobby
Quote:

Originally Posted by djmccabie
given that f(x) = e^x - x - 1, show that f is an increasing function for x>0

OK i can see that this statement is true... but i just don't know how to write it on paper...

Do you not just differentiate it, and show that is is > 0 on $(1,\infty)$??

So $f'(x) = e^x - 1$

$e^x > 0$ and $e^x > 1$ for x > 0

$f'(x) > 0$ for $x>0$

Therefore

$f(x)$is an increasing function..

Sound right?