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

Relatively easy limit help please

  • Thread starter Hessam
  • Start date
36
0
ok... so i'm taking calc3, and didnt go to class for a month, lol

now i can't solve this (what seems like) a simple limit... please help


lim
(x,y,z) -> (0,0,0)

of this

xy + yz + zx
-----------------
(x^2)+(y^2)+(z^2)




i tried doing the limit as (x,y,z) approaches (x,0,0) (0,y,0) and (0,0,z) and got zero, but that's not the answer

however when i put it into my calc and grind it out i get 1... but how can i do it on paper?

thankyou very much in advance
 
Last edited:
92
0
The limit does not exist

To show that, take two curves, e.g:

[tex]x=y=z[/tex] and [tex]x=y=-z[/tex]

You'll find [tex]\frac {3x^2} {3x^2}[/tex] and [tex]\frac {-x^2} {3x^2}[/tex]

Whose limits are 1 and [tex]-\frac {1} {3}[/tex], which are different. CVD
 

Related Threads for: Relatively easy limit help please

Replies
12
Views
2K
Replies
4
Views
1K
  • Posted
Replies
2
Views
1K
Replies
3
Views
5K
  • Posted
Replies
1
Views
2K
Replies
16
Views
2K
Replies
2
Views
855

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top