September 26th, 2013, 06:37 AM  #1 
Newbie Joined: Sep 2013 Posts: 1 Thanks: 0  Showing limit equals derivative
This is giving me so much trouble and I have no idea why. I just have to show that f'(x) = ( f(x + e)  f(x  e) ) / 2e for x = 5 and e = .001 The actual function is f(x) = e^(sinx) + xln(3 + cosx) and I'm almost positive the derivative is f'(x) = cos(x)e^(sinx) + ln(3 + cosx)  xsinx/(3 + cosx) When I evaluate the derivative at 5 I get 2.363208918 but when I evaluate the function with the small e I get 1.402409569 I just can't figure out why these numbers don't match up. Thanks. 
September 26th, 2013, 09:45 AM  #2 
Senior Member Joined: Jul 2012 From: DFW Area Posts: 635 Thanks: 96 Math Focus: Electrical Engineering Applications  Re: Showing limit equals derivative
Hi jpanderson8, and welcome to the forums. I think that the derivative is correct, however, I think you are making the calculation using degrees. If you use radians, you should get 2.75783 (for both calculations). Also, I know that it is difficult without using but just to make sure let me restate: . 

Tags 
derivative, equals, limit, showing 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
In what situation frac of limits equals to limit of frac?  stainburg  Calculus  17  November 24th, 2013 12:14 AM 
prove this limit equals 0  yogazen2013  Calculus  2  October 5th, 2013 08:44 AM 
Showing a limit does not exist?  ArtMajorTakingCalc  Calculus  11  July 21st, 2012 08:03 AM 
derivative/limit  kaka2012sea  Real Analysis  1  November 11th, 2011 08:52 AM 
Showing there is a limit cycle  lu5t  Applied Math  0  June 3rd, 2011 07:19 PM 