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Thread Subject:
i can't integrate this function, please help!!!

Subject: i can't integrate this function, please help!!!

From: maneerat

Date: 5 May, 2012 01:18:30

Message: 1 of 4

i can't integrate this function !!!
f(x)=1/(((1-x)^0.25)((Z-3*x)^0.25))
integrate from 0 to x and Z is constant value
i don't know which code i should use to solve this function

i used
>>int(1/(((1-x)^0.25)((Z-3*x)^0.25)),x)

but it showed that "Warning: Explicit integral could not be found."
  
please help me!
thanks

Subject: i can't integrate this function, please help!!!

From: Nasser M. Abbasi

Date: 5 May, 2012 03:19:41

Message: 2 of 4

On 5/4/2012 8:18 PM, maneerat wrote:
> i can't integrate this function !!!
> f(x)=1/(((1-x)^0.25)((Z-3*x)^0.25))
> integrate from 0 to x and Z is constant value
> i don't know which code i should use to solve this function
>
> i used
>>> int(1/(((1-x)^0.25)((Z-3*x)^0.25)),x)
>
> but it showed that "Warning: Explicit integral could not be found."
>
> please help me!
> thanks


write 1/4 and not 0.25 ! This made the code go via
a symbolic path internally, much easier on the poor symbolic
engine ;)

ps. and you got too many extra paranthesis, not needed.
And it always better to break down the terms a little, to
make it easier on the eyes to see things:

-----------------------------
clear all
syms x Z;
den = (1-x)^1/4 * (Z-3*x)^1/4;
int( 1 /den ,x)
------------------------------

ans =
  
(16*log((Z - 3*x)/(x - 1)))/(Z - 3)
  

--Nasser

Subject: i can't integrate this function, please help!!!

From: Roger Stafford

Date: 5 May, 2012 04:39:29

Message: 3 of 4

"Nasser M. Abbasi" <nma@12000.org> wrote in message <jo268r$hd0$1@speranza.aioe.org>...
> write 1/4 and not 0.25 ! This made the code go via
> a symbolic path internally, much easier on the poor symbolic
> engine ;)
>
> ps. and you got too many extra paranthesis, not needed.
> And it always better to break down the terms a little, to
> make it easier on the eyes to see things:
>
> -----------------------------
> clear all
> syms x Z;
> den = (1-x)^1/4 * (Z-3*x)^1/4;
> int( 1 /den ,x)
> ------------------------------
>
> ans =
>
> (16*log((Z - 3*x)/(x - 1)))/(Z - 3)
>
> --Nasser
- - - - - - - - - -
  If you differentiate that indefinite integral, Nasser, you will get this for an answer:

 16/((Z-3*x)*(1-x))

which is equal to

 1/(((1-x)^1)/4*((Z-3*x)^1)/4)

  The symbolic toolbox played a trick on you. It didn't recognize

 (1-x)^1/4 and (Z-3*x)^1/4

the way you intended. You need parentheses around the 1/4 in each factor.

Roger Stafford

Subject: i can't integrate this function, please help!!!

From: Nasser M. Abbasi

Date: 5 May, 2012 05:19:41

Message: 4 of 4

On 5/4/2012 11:39 PM, Roger Stafford wrote:
> "Nasser M. Abbasi"<nma@12000.org> wrote in message<jo268r$hd0$1@speranza.aioe.org>...
>> write 1/4 and not 0.25 ! This made the code go via
>> a symbolic path internally, much easier on the poor symbolic
>> engine ;)
>>
>> ps. and you got too many extra paranthesis, not needed.
>> And it always better to break down the terms a little, to
>> make it easier on the eyes to see things:
>>
>> -----------------------------
>> clear all
>> syms x Z;
>> den = (1-x)^1/4 * (Z-3*x)^1/4;
>> int( 1 /den ,x)
>> ------------------------------
>>
>> ans =
>>
>> (16*log((Z - 3*x)/(x - 1)))/(Z - 3)
>>
>> --Nasser
> - - - - - - - - - -
> If you differentiate that indefinite integral, Nasser, you will get this for an answer:
>
> 16/((Z-3*x)*(1-x))
>
> which is equal to
>
> 1/(((1-x)^1)/4*((Z-3*x)^1)/4)
>
> The symbolic toolbox played a trick on you. It didn't recognize
>
> (1-x)^1/4 and (Z-3*x)^1/4
>
> the way you intended. You need parentheses around the 1/4 in each factor.
>
> Roger Stafford

good point Roger, I removed too many paranthesis.

yes, x^1/4 != x^(1/4) :)

And I did not bother to differentiate to check the computer
did it right. I should have.

thanks

--Nasser

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