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Integral problem

  • Thread starter dnt
  • Start date
  • #1
dnt
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Homework Statement



how do you integrate (xcox)dx

Homework Equations



n/a

The Attempt at a Solution



ive gone through so many ways that ive learned how to integrate problems and i cannot figure this one out. can someone just give me a hint on how to start it? thanks. (i have a feeling this is easy and im overlooking a really basic way of doing it)
 

Answers and Replies

  • #2
VietDao29
Homework Helper
1,423
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When seeing a product of a polynomial and ex, or some kind of trigonometry functions. One should think about Integrate by Parts.
By letting u = the polynomial, in this case u = x.
And dv = the rest.
By the way, is your problem:
[tex]\int x \cos x dx \quad \mbox{or} \quad \int x \cot x dx[/tex]?
Can you go from here? :)
 
  • #3
2,063
2
Integration by parts.
 
  • #4
2,063
2
By letting u = the polynomial, in this case u = x.
And dv = the rest.
I do not know if this mnemonic is taught everywhere, but when I was in school learning integration by parts, we were asked to remember ILATE, without justification, when deciding which part is to be u and which is to be dv. Of course, this rule need not work every time.

Inverse(Trigonometric)-Logarithmic-Algebraic-Trigonometric-Exponential.

The one that comes before the other will be u.
 
  • #5
dnt
238
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thanks. i knew it was easier than i thought.

and btw it was cos (forgot the s)
 
  • #6
VietDao29
Homework Helper
1,423
1
I do not know if this mnemonic is taught everywhere, but when I was in school learning integration by parts, we were asked to remember ILATE, without justification, when deciding which part is to be u and which is to be dv. Of course, this rule need not work every time.

Inverse(Trigonometric)-Logarithmic-Algebraic-Trigonometric-Exponential.

The one that comes before the other will be u.
Well, yes, some of the textbooks here do mention it. However, the are very rare, I think.
Btw, I don't know what it's called in English. Since, I am not a native-English speaker. Still have to learn a lot. :blushing:
So yeah, thanks for the info. :)
 

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