
Calculus Calculus Math Forum 
 LinkBack  Thread Tools  Display Modes 
March 18th, 2009, 01:53 PM  #1 
Member Joined: Mar 2009 From: San Bernardino, California Posts: 50 Thanks: 0  Quick Second Partial Derivative Test Question
I understand that when the discriminant of a function defined as is less than zero at point (a,b) then the function has a saddle point at (a,b) and if the discriminant is greater than zero at (a,b) there exists a local extrema at point (a,b) (D=0 is inconclusive). Also if there is a local extrema then: there exists a local minimum at (a,b) there exists a local maximum at (a,b) However what about the case that D>0 at (a,b) indicating that there is a local extrema, but ? This can't be a saddle point can it? Or does the test fail? 
March 19th, 2009, 12:38 AM  #2 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: Quick Second Partial Derivative Test Question
In that case look at instead. Also: the singular is extremum, the plural is extrema. 
March 19th, 2009, 08:51 PM  #3 
Member Joined: Mar 2009 From: San Bernardino, California Posts: 50 Thanks: 0  Re: Quick Second Partial Derivative Test Question
Ahh ok thank you. Is there any particular reason we choose to evaluate first rather than ?

March 19th, 2009, 10:21 PM  #4 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: Quick Second Partial Derivative Test Question
No. You can check any directional derivative.


Tags 
derivative, partial, question, quick, test 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Partial Derivative Question  Jerkin' My Gherkin  Calculus  3  March 17th, 2014 10:24 AM 
First Derivative Test  SamFe  Calculus  1  November 7th, 2013 01:04 PM 
Partial Derivative Question  kevinp123  Calculus  0  September 20th, 2011 05:32 AM 
quick&easy  distributive property, partial fractions  mbradar2  Calculus  3  November 23rd, 2010 04:21 PM 
Quick derivative question  funsize999  Calculus  6  March 29th, 2009 09:53 PM 