You are Here: Home

# finding the limit watch

1. find the limit as x->pi/2 of:

(cosh x -1)/(x tanx)

that tanx is giving me grief. using its power series (expanded about pi/2) doesnt help, as its derivatives etc are undefined. the same goes for trying l'hopital's rule. i thought about using power series expanded about pi/4, but that might give inaccurate results (pi/4 ~= 0.78, which is a lot bigger than 0.1 or the general accuracy concensus).
2. (Original post by elpaw)
find the limit as x->pi/2 of:

(cosh x -1)/(x tanx)

that tanx is giving me grief. using its power series (expanded about pi/2) doesnt help, as its derivatives etc are undefined. the same goes for trying l'hopital's rule. i thought about using power series expanded about pi/4, but that might give inaccurate results (pi/4 ~= 0.78, which is a lot bigger than 0.1 or the general accuracy concensus).

At a guess => 1/tanx => 0 ??? Just because the tanx term will dominate all the others?
3. (Original post by Lagz)
At a guess => 1/tanx => 0 ??? Just because the tanx term will dominate all the others?
Yes.

(cosh(x) - 1) / x is bounded as x -> pi/2.

1 / tan(x) -> 0 as x -> pi/2.

So the product of these two things -> 0 as x -> pi/2.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 27, 2004
Today on TSR

### Are you living on a tight budget at uni?

From budgets to cutbacks...

### University open days

1. University of Cambridge
Wed, 26 Sep '18
2. Norwich University of the Arts
Fri, 28 Sep '18
3. Edge Hill University
Faculty of Health and Social Care Undergraduate
Sat, 29 Sep '18
Poll

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE