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Integration help

Can someone explain how i'd do the integral below please?
I know it's by parts but I have no clue how in this caseBD4B44D1-2D35-4D37-BBC7-66852AFCD85D.jpeg
(edited 2 years ago)
Reply 1
A bit like the cos() and sin() pairing (derivative and pythagorean identity), tan() and sec^2() have a similar relationship so cot() and .... So think how the trig terms are related, then when you do the parts, you want to differentate the x^2 and integrate the trig term(s)?
(edited 2 years ago)
Reply 2
Original post by mqb2766
A bit like the cos() and sin() pairing (derivative and pythagorean identity), tan() and sec^2() have a similar relationship so cot() and .... So think how the trig terms are related, then when you do the parts, you want to differentate the x^2 and integrate the trig term(s)?

Oh so you mean 1+cot²=cosec² , so the trig parts simplify to cot³x- cotx , so I can split it into 2 integrals?
And yes I'm differentiating the and integrating the trig

If it is the case, I've gone terribly wrong as I'm now stuck in an infinite integration loop with the 2nd integral :/
545CFF6A-7D9E-458F-91AE-C0A002C59110.png
(edited 2 years ago)
Reply 3
No, use the derivative relatisnhip s0
d cot(x)/dx = - cosec^2(x)
Reply 4
Original post by mqb2766
No, use the derivative relatisnhip s0
d cot(x)/dx = - cosec^2(x)

Use it how?
LIATE so u=x² and dv/dx = cosec²xcotx
Du/dx = 2x And to get v do we then integrate by reverse chain rule as it's f'(x)f(x) ?
(edited 2 years ago)
Reply 5
You want to integrate
f'(x)f(x)
So the integral should be cosec^2().
(edited 2 years ago)
Reply 6
Original post by mqb2766
You want to integrate
f'(x)f(x)
So the integral should be cosec^2().

Meaning dv/dx = cosec²x and u is 2x²cotx ?
Original post by Rhys_M
Meaning dv/dx = cosec²x and u is 2x²cotx ?

no you were right the first time.

If you're stuck on how to integrate cotxcosec^2x, consider the substitution u=cotx.
(edited 2 years ago)
Reply 8
Original post by JustSomeGuy:/
no you were right the first time.

If you're stuck on how to integrate cotxcosec^2x, consider the substitution u=cotx.

Yea That's what I thought - I was then doing that subsitution. Thank you

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