Integration by Parts: Solving \int t sin(2t) dt

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SUMMARY

The discussion focuses on solving the integral \(\int t \sin(2t) dt\) using the integration by parts formula \(\int u dv = uv - \int v du\). The user initially selects \(u = t\) and \(dv = \sin(2t) dt\), leading to a complex expression involving \(\int \sin^2(t) dt\). A more efficient approach is suggested, utilizing the substitution \(u = 2t\) to simplify the integration process. This method significantly streamlines the solution and avoids complications associated with integrating \(\sin^2(t)\).

PREREQUISITES
  • Understanding of integration techniques, specifically integration by parts.
  • Familiarity with trigonometric identities, particularly the double angle formulas.
  • Knowledge of substitution methods in integral calculus.
  • Basic proficiency in manipulating integrals involving trigonometric functions.
NEXT STEPS
  • Study the integration by parts technique in greater depth.
  • Learn how to apply the double angle formulas for trigonometric functions.
  • Explore substitution methods for simplifying integrals, particularly with trigonometric functions.
  • Practice integrating various forms of \(\sin(kx)\) and \(\cos(kx)\) using different techniques.
USEFUL FOR

Students studying calculus, particularly those focusing on integral calculus and integration techniques, as well as educators seeking to clarify integration by parts and substitution methods.

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Homework Statement



\int t sin(2t) dt

Homework Equations



Integration by parts formula:

\intudv = uv - \intvdu

The Attempt at a Solution



I chose t to be u so,

u=t
du=dt
dv=sin(2t)dt
v=(sin)^2 (hope that's right. I used double angle formula to change sin(2t) into 2sint cost)

So now by the integration by parts formula I get:


\intt sin(2t)dt = t(sint)^2 - \int(sint)^2 dt

Now I have no idea how to integrate sin2t

I don't know if I messed up somewhere way up there or if it's right and I'm just stuck on this part. Any help would be greatly appreciated. Thanks in advance!
 
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You integrate sin(t)^2 by using the double angle approach again. But the whole thing is a lot easier if you integrate sin(2t) just using the substitution u=2t.
 
Wow thanks Dick I can't believe I overlooked that. Also, thanks a lot for the prompt reply!
 

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