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Determining the stationary points of f(x)

Hi, this is my first post here!
I've been looking at some past examples to determine the stationary points of f(x), but keep coming into errors wherever I look. 'm' is saved so shouldn't cause any issues, I just cant get past the issues with 'x'

The equation is : f(x) = (5*x^2)/(m(x^2+1))

Initially I tried:
>> f=(5*x^2)/(m(x^2+1))
Undefined function or variable 'x'.

Followed by (purely guessing to see if I could get it to work:
>> syms x
>> f=(5*x^2)/(m(x^2+1))
Error using sym/subsindex (line 766)
Invalid indexing or function definition. When defining a function, ensure that the arguments are symbolic variables and the body
of the function is a SYM expression. When indexing, the input must be numeric, logical, or ':'.


I seem unable to get past this, and any help would greatly be appreciated
0
Lmore
12/20/2016 1:08:03 PM
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On 12/20/2016 7:08 AM, Lmore wrote:
> Hi, this is my first post here!
> I've been looking at some past examples to determine the stationary points of f(x),
>but keep coming into errors wherever I look. 'm' is
>saved so shouldn't cause any issues, I just cant get past the issues with 'x'
>
> The equation is : f(x) = (5*x^2)/(m(x^2+1))
>
> Initially I tried:
>>> f=(5*x^2)/(m(x^2+1))
> Undefined function or variable 'x'.
>
> Followed by (purely guessing to see if I could get it to work:
>>> syms x
>>> f=(5*x^2)/(m(x^2+1))
> Error using sym/subsindex (line 766)
> Invalid indexing or function definition. When defining a function,
>ensure that the arguments are symbolic variables and the body
> of the function is a SYM expression. When indexing, the input must
>be numeric, logical, or ':'.
>
>
> I seem unable to get past this, and any help would greatly be appreciated
>


One way might be

clear
syms x m
f=(5*x^2)/(m*(x^2+1));
df=diff((5*x^2)/(m*(x^2+1)),x)
  
      (10*x)/(m*(x^2 + 1)) - (10*x^3)/(m*(x^2 + 1)^2)
  
solve(df==0,x)
   
    0



0
Nasser
12/20/2016 9:00:35 PM
Reply: