integration

Papabravo

Joined Feb 24, 2006
21,228
In your first attempt you are doing things which are not allowed.

\((x-x^3)^{\frac13}\quad \ne \quad x^{\frac13}-x\)
 
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Thread Starter

GMChandio

Joined Feb 26, 2015
28
How can i solve further without simplifying?
Besides i only know this method to solve problems, simplify and apply the formula.
 

WBahn

Joined Mar 31, 2012
30,077
Your very first step shows that you have a fundamental weakness in your algebra skills. You start of by asserting that

\(
{\(x-x^3\)}^{\frac{1}{3}} \, = \, x^{\frac{1}{3}}-x
\)

By this line of reasoning,

\(
{\(a+b)}^{2} \, = \, a^2 + b^2
\)

Do you agree with this?

If you do, then just set a=b=1 and see if it actually works out.
 

WBahn

Joined Mar 31, 2012
30,077
One route you can go is to just differentiate the possible answers and see which one yields the original integrand. I would do the one that has "+1+C" last since the 1 could be absorbed into the C which means that this answer is probably a distractor.
 

Papabravo

Joined Feb 24, 2006
21,228
So that simplification will not work. You'll have to find another one.
As an aid to figuring this out did it occur to you to differentiate one or more of the answers?
Also if you can get the integral into the form

\(\int u\cdot du\)
then maybe you can solve it.
 
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Thread Starter

GMChandio

Joined Feb 26, 2015
28
One route you can go is to just differentiate the possible answers and see which one yields the original integrand. I would do the one that has "+1+C" last since the 1 could be absorbed into the C which means that this answer is probably a distractor.
That would take a lot of time, differentiating all the options
 

Thread Starter

GMChandio

Joined Feb 26, 2015
28
So that simplification will not work. You'll have to find another one.
As an aid to figuring this out did it occur to you to differentiate one or more of the answers?
If you can get the integrand into the form

\(\int u\cdot du\)
then maybe you can solve it.
Differentiating all the options ia going to take alot of time, and iam going to get just over a minute to solve this kind of queation, i've got a test coming up in no time.
 

WBahn

Joined Mar 31, 2012
30,077
That would take a lot of time, differentiating all the options
Really? I did it in less than three minutes.

Look at the three options -- they all have the same primary component, namely

\(
{\( \frac{1}{x^2} - 1\)}^{\frac{4}{3}}
\)

How hard can it be?
 

Thread Starter

GMChandio

Joined Feb 26, 2015
28
Really? I did it in less than three minutes.

Look at the three options -- they all have the same primary component, namely

\(
{\( \frac{1}{x^2} - 1\)}^{\frac{4}{3}}
\)

How hard can it be?
It maybe easy for you.
But the answer is C, not A.
 

WBahn

Joined Mar 31, 2012
30,077
Let me walk you through it one step at a time.

What is

\(
\frac{d}{dx}\[{\( \frac{1}{x^2} - 1\)}^{\frac{4}{3}}\]
\)

I picked this form instead of the (1 - 1/x^2) form simply because this is the form used in two of the three potential answers. But hopefully you recognize that the differ only by a minus sign.
 
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