I know according to rule 5 of the law of limits, this cant work by substition because the denominator would equal 0. I know i need to start this off by factoring but im not sure how to start this process.
Oct 5th 2009, 04:26 PM
I think the next step would look somethin like this..
...but im not exactly positive.
Oct 5th 2009, 05:33 PM
That's correct. Continue on.
Oct 5th 2009, 05:41 PM
I got it, i made a mistake swapping a + sign for a -.... Thank you!
Oct 6th 2009, 04:13 AM
Remember that when x= a makes polynomial P(x) zero- that is if P(a)= 0, then x-a must be a factor of P(x). Here, you saw correctly that the denominator is 0 when x= 2. That should make you look immediately at the numerator!
If the numerator were NOT 0 at x= 2, that would tell you that the limit does not exist and you can stop.
If the numerator is 0 at x= 2, which is the case here, , you know that you can factor out x-2. Once you know that, it should be clear that .
Now you can think as long as .
Notice that "as long as ". Of course, is "undefined" at x= 2 while x+3 is equal to 5 at x= 2 so we cannot just say that . Fortunately there is an (often overlooked) theorem about limits that says "If f(x)= g(x) for all x except x=a, then ".
Knowing that for all x except x= 2 is enough to tell us they have the same limit at x= 2 and, of course, is easy.
Oct 6th 2009, 10:31 AM
great tip, i wasnt aware of that trick to determine if there is a limit! Awsome, i love this place.