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

Finding x

  • Thread starter Toby_Obie
  • Start date
  • #1
19
0
Hello,

Im trying to rearrange to find x from the below (all other values, A, b and c known)

[tex] A = bx / 1-(1+x)^-c [/tex]

Below denominator ending reads (1+x)^(-c)

I've rearranged but to no avail, I'm unsure how to isolate x

Any input much appreciated

Thanks
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
25,832
250
Hello Toby! :smile:

(you needed to put the index in curly brackets, {-c}, since it had more than one character … alternatively, try using the X2 tag just above the Reply box :wink:)

This is the same as (1 + x)-c = 1 - (b/A)x …

I don't think there is a "simple" solution.

But why are you looking for one?
 
  • #3
19
0
Noted

I've never come up against an equation like this before, just curious whether it can be solved for x ? (new skills)

Is there a general solution to this type of equation ?

Can you point me in the right direction ?

Thanks very much
 
  • #4
tiny-tim
Science Advisor
Homework Helper
25,832
250
Is there a general solution to this type of equation ?
I don't think so.

Real life just isn't that convenient! :redface:
 
  • #5
19
0
Thanks anyway

Anybody else think they know the answer ?
 
  • #6
Mentallic
Homework Helper
3,798
94
Really, the problem is very complicated to solve, and for most [itex]c\geq 4[/itex] it's likely impossible to solve!

There is a proof that says for polynomials of degree 5 or higher, there is no way to solve the equation in its general case like quartics and below have been.
 
  • #7
19
0
Okay

I'm using Excel to approximate x for known values of A, b, c

Thanks anyways
 
  • #8
19
0
Just a note

Excel Goal Seek function solved my function to 4 decimal places, good tool
 

Related Threads on Finding x

  • Last Post
Replies
6
Views
1K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
10
Views
1K
  • Last Post
Replies
9
Views
1K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
3
Views
9K
  • Last Post
Replies
7
Views
1K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
7
Views
16K
Top