• Support PF! Buy your school textbooks, materials and every day products Here!

Estimating partial derivatives

  • Thread starter joemama69
  • Start date
  • #1
399
0

Homework Statement



a metal plate is situated in the xy plane and occupies the rectangle 0<x<10 and 0<y<8 where x a y are measure in meters. The temperature oat the pooint x,y on the plate it T(x,y), where T is measured in degrees celcius.
note the attached table

a- estimate the values of teh partial derivatives of Tx(6,4) and Ty(6,4). What are the units of measure
b - Estimate the values of Tu(6,4) where u = (i + j)/(2^1/2). Interpret your result
c - Estimate the value of Txy(6,4)


Homework Equations





The Attempt at a Solution



welp im not sure if correct but hers what i did

a - t(x) = 6, because from point 6,4, moving down the x value the temp rises 6 degrees
and so t(y) = -5. the units are degrees celsius i belive

b - for b i pluged my x and y partials from part a into the i & j component and got u = 7.8 degrees celcius

c - t(x) = 6 just as in part a. and from there point 8,4, i moved the right for a change of -6 degrees
 

Attachments

Answers and Replies

  • #2
HallsofIvy
Science Advisor
Homework Helper
41,794
925

Homework Statement



a metal plate is situated in the xy plane and occupies the rectangle 0<x<10 and 0<y<8 where x a y are measure in meters. The temperature oat the pooint x,y on the plate it T(x,y), where T is measured in degrees celcius.
note the attached table

a- estimate the values of teh partial derivatives of Tx(6,4) and Ty(6,4). What are the units of measure
b - Estimate the values of Tu(6,4) where u = (i + j)/(2^1/2). Interpret your result
c - Estimate the value of Txy(6,4)


Homework Equations





The Attempt at a Solution



welp im not sure if correct but hers what i did

a - t(x) = 6, because from point 6,4, moving down the x value the temp rises 6 degrees
and so t(y) = -5. the units are degrees celsius i belive
What is "t"? Is it the same as T? If so, what do you mean by T(x)? T is a function of both x and y. Do you mean Tx(x,y), the derivate with respect to x?

The temperature at (6,4) is 80 while the termperatures at (4, 4) and (8,4) are 78 and 96 respectively. you could estimate the rate of temperature there as (80- 78)/(6-4)= 1 or (96- 80)/(8- 6)= 3 or (96- 78)/(8- 4)= 2. Of those I would expect the last to be most accurate. You seem to have forgotten to divide by the "[itex]\Delta x[/itex]".

Finally, the units are not "degrees celcius". Because this is a rate of change, the units are "degrees celcius per meter"- again, you did not divide by the "[itex]\Delta x[/itex]".

b - for b i pluged my x and y partials from part a into the i & j component and got u = 7.8 degrees celcius
Did you divide by [itex]\sqrt{2}[/itex]?

c - t(x) = 6 just as in part a. and from there point 8,4, i moved the right for a change of -6 degrees
This question is asking for a second derivative. Calculate the partial derivatives with respect to x at (6,4), (6,2), and (6,6), then do the same calculation for the partial derivative with respect to y.
 
Last edited by a moderator:
  • #3
399
0
sorry i was being lazy t(x) was just the partial with respect to x

ok so heres what i did

T(x) = (86 - 80)/(8-6) = 3
T(y) = (75-80)/(6-4) = -2.5

T(u), where u = (i + j)/21/2 was i corect in saying that i = T(x) & j = t(y), so T(u) = .354

for T(xy) dont i have to take the partial T(x), and then partial that with respect to y.

how do i do that.
 
  • #4
399
0
Ok I think i got Txy(6,4)

Tx(6,4) = 3
Tx(6,6) = 2.5

=(Tx)(6,6) - Tx(6,4))/delta T = (3-2.5)/2 = .25

Can i get a ahmen
 

Related Threads for: Estimating partial derivatives

Replies
1
Views
7K
Replies
5
Views
964
  • Last Post
Replies
4
Views
744
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
0
Views
2K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
6
Views
1K
Top