Evaluate the limit   lim(x-->pi+)  (cosx)/(x-pi)

Asked on by bdremm

1 Answer | Add Yours

lfryerda's profile pic

lfryerda | High School Teacher | (Level 2) Educator

Posted on

To evaluate this limit, we try direct substitution before anything else, and see that letting `x->pi^+` gives `-1/0`

which is undefined, so we know that the limit as `x->pi` does not exist.  However, the right side will either go to positive or negative infinity.

Let `x=pi+epsilon` where `epsilon` is a small real positive number.

Then `cos(pi+epsilon)=cos pi cos epsilon-sin pi sin epsilon`

which becomes:

`-cos epsilon<0`

Also, the denominator of the limit is:




This means that the limit is a negative number, and so we have:

The right-sided limit is negative infinity.

We’ve answered 319,816 questions. We can answer yours, too.

Ask a question