Need help with Calculus 3

[dennisjmathew]

Suppose u (x,y) is twice differentiable and define new variable
? = x + t , ? = x – t
show that (?^2 u)/(?^2 x)-(?^2 u)/(?^2 t)=(?^2 u )/???

 

[Deleted member 4993]

Suppose u (x,y) is twice differentiable and define new variable
? = x + t , ? = x – t
show that (?^2 u)/(?^2 x)-(?^2 u)/(?^2 t)=(?^2 u )/???

First make sure you have correctly copied the problem - pay extra attention to the independant variables.

Then read "Read Before Posting"

Then:

Please share your work with us indicating exactly where you are stuck - so that we may know where to begin to help you.

 

[dennisjmathew]

I just re-checked the problem. It is exactly how I copied. My problem is that I just cannot define 'u'. Thus I am unable to diffrentiate with respect to t. I am in Calculus 3. I was assigned this problem as an extra credit assignment for the chapter 'Partial derivatives'

 

[dennisjmathew]

This looks like a theorem/proof to me ... but I checked the last couple of pages of my textbook where all the proofs are given and I din't find anything related.