Definite Integral of Trig Function

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SUMMARY

The discussion focuses on the definite integral of the function ∫sin(2x)cos(x) from x=0 to x=π/4. The solution employs the double angle identity, transforming the integral into ∫2sin(x)cos²(x) and utilizing the substitution u=cos(x), leading to the evaluation of the integral as -2cos³(x)/3. The final result for the integral at x=π/4 is -1/(3√2), while the value at x=0 is calculated as (-1+2√2)/3√2. The participants confirm the correctness of the solution and engage in light-hearted banter.

PREREQUISITES
  • Understanding of trigonometric identities, specifically the double angle formulas.
  • Familiarity with integration techniques, including substitution and integration by parts.
  • Knowledge of definite integrals and their evaluation over specified limits.
  • Basic skills in manipulating algebraic expressions involving square roots.
NEXT STEPS
  • Study the application of trigonometric identities in integration, focusing on double angle formulas.
  • Learn advanced integration techniques, such as integration by parts and trigonometric substitution.
  • Explore the properties of definite integrals and their geometric interpretations.
  • Practice solving integrals involving products of trigonometric functions using substitution methods.
USEFUL FOR

Students studying calculus, particularly those focusing on integration techniques, as well as educators looking for examples of definite integrals involving trigonometric functions.

Jimbo57
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Homework Statement


∫sin2xcosx x=0,pi/4


Homework Equations





The Attempt at a Solution


By double angle magic:
∫sin2xcosx=
∫2sinxcos^2x
u=cosx
du=-sinxdx
-2∫u^2
-2(u^3)/3
-2cos^3x/3
= -1/(3√2) for x=pi/4

How does that look folks?
 
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Hi Jimbo57! :smile:

(have a pi: π and try using the X2 button just above the Reply box :wink:)

Fine down to …
Jimbo57 said:
-2cos^3x/3
= -1/(3√2) for x=pi/4

… what about for x = 0 ? :wink:
 
tiny-tim said:
Hi Jimbo57! :smile:

(have a pi: π and try using the X2 button just above the Reply box :wink:)

Fine down to …


… what about for x = 0 ? :wink:


Lol woops, I'm used to ignoring the 0 with non trig integrals.

New answer:

(-1+2√2)/3√2

Thanks for the help Tiny-Tim! (and the pi)
 

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