View Single Post
Feb24-10, 03:15 PM
P: 42
1. The problem statement, all variables and given/known data

Lim [2 + 3x + sin(x)] / [x + 2cos(x)]

2. Relevant equations

3. The attempt at a solution

My roommate asked me to help him solve this homework question, at first glance I noted the derivative to be:

[3 + cos(x)] / [1 - 2sin(x)]

Now, the next step I'm assuming would be to plug infinity in for x. The answer in the book says that this should reduce the equation to 3. This would mean that by substituting infinity for x, the cos(x)/2sin(x) has to reduce to 1. But if x is approaching infinity, wouldn't a sin or cos wave just go back and forth between -1 and 1 forever? How, mathematically speaking, is it justifiable to say that they'd reduce to 1?

Phys.Org News Partner Science news on
Mysterious source of ozone-depleting chemical baffles NASA
Water leads to chemical that gunks up biofuels production
How lizards regenerate their tails: Researchers discover genetic 'recipe'