One equation one unknown

  • Thread starter sara_87
  • Start date
  • #1
763
0

Homework Statement


i want to find the value of k in the following equation:
8.7-(0.75/k)=[e^(8k)](11.7-(0.75/k))


Homework Equations





The Attempt at a Solution



i know i can use matlab but i dont have matlab and i dont even know how to do it on matlab; does anyone know how to do it on matlab?
is there an alternative method to find k?

thank you
 

Answers and Replies

  • #2
Dick
Science Advisor
Homework Helper
26,263
619
If you don't have any special tools, write the problem as f(k)=exp(8*k)*(11.7-.75/k)-(8.7-0.75/k). Now you want to find where f(k)=0. Now graph it and look for a zero, or just try different values of k until you find one where f(x) is positive and one where it's negative. E.g. f(0.03)<0 and f(0.04)>0. That means there is a root between 0.03 and 0.04. Try the midpoint k=0.035 and keep refining the interval containing the root until you get enough significant digits for the needs of the problem. This is called 'bisection'.
 
  • #3
763
0
yes i know that method but it takes too long and i'm lazy.
i just need the answer without the working out so i dont want to take too much time finding the value for k.
 
  • #4
cristo
Staff Emeritus
Science Advisor
8,122
74
yes i know that method but it takes too long and i'm lazy.
i just need the answer without the working out so i dont want to take too much time finding the value for k.

Well, you should just probably wait until you get to a computer with maple or matlab or whatever. Otherwise, you'll need to do it the long way!
 
  • #5
HallsofIvy
Science Advisor
Homework Helper
41,847
966
There is no simple formula for such a problem. You might be able use the Lambert W function, but I suspect just getting it into the right form for that would be much more work that the graph Dick suggested.
 
  • #6
763
0
yes but how do i type that into matlab and how do i find k using matlab? what do i type?
 

Related Threads on One equation one unknown

Replies
9
Views
2K
  • Last Post
Replies
2
Views
8K
Replies
5
Views
2K
  • Last Post
Replies
2
Views
11K
  • Last Post
Replies
6
Views
3K
  • Last Post
Replies
4
Views
3K
Replies
2
Views
975
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
1
Views
3K
Top