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Mathematics Forum

Author	Message / Information
Grogler Quote \| Reply \|	Second-order differentiation posted on: 11/22/2006 9:55:51 AM Suppose I have: u = x^3 + y^3 - 3xy(x - y) Can I write: du = (3x^2 - 3y(x - y) - 3xy)*dx ??? And, please, help me to find u''. Thanks in advance.
Euler Quote \| Reply \|	Second-order differentiation replied on: 11/22/2006 2:53:27 PM It depends- the equation you got for du is correct if you do the partial derivative of u with respect to x; however, you could also get: du/dy=3y^2-3x(x-y)+3xy As, for the second derivative, it depends on what varible you are doing the partial derivative with respect to. If you take your du equation and differentiate with respect to x you get: u''=6x-6y, and if you do it with respect to y you get: u''=-6x+6y
Euler Quote \| Reply \|	Second-order differentiation replied on: 11/22/2006 3:03:19 PM I should also point out that if you differentiate the equation I gave for du/dy, again- you would get identical answers.
Grogler Quote \| Reply \|	Second-order differentiation replied on: 11/23/2006 11:08:19 AM Thanks
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