How to Integrate cos4 x Using the Double Angle Formula

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SUMMARY

The integral of cos4 x can be effectively solved using the double angle formula. By expressing cos4 x as (cos2 x)² and applying the identity cos2 x = (cos2 x + 1)/2, the integral can be simplified into manageable parts. The final result of the integration is (sin4 x)/32 + (sin2 x)/4 + (3x)/8 + C, confirming the correctness of the approach taken. This method demonstrates the utility of trigonometric identities in solving integrals.

PREREQUISITES
  • Understanding of trigonometric identities, specifically cos2 x.
  • Familiarity with integration techniques in calculus.
  • Knowledge of the double angle formulas for cosine.
  • Ability to manipulate algebraic expressions involving trigonometric functions.
NEXT STEPS
  • Study the derivation and application of the double angle formulas for sine and cosine.
  • Practice integrating various trigonometric functions using identities.
  • Explore advanced integration techniques such as integration by parts and substitution.
  • Learn about the applications of trigonometric integrals in physics and engineering.
USEFUL FOR

Students studying calculus, particularly those focusing on integration techniques, as well as educators teaching trigonometric identities and their applications in solving integrals.

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Homework Statement



Find the integral of cos4 xdx

Homework Equations



cos2x = 2cos2x-1
cos2x = (cos2x+1)/2

The Attempt at a Solution



I tried using cos4x = cos2x * cos2x and i simplified it to
cos4x = ((cos2x)2 + 2cos2x + 1)/4

I'm not sure if this is right. How do i go about getting the integral of this expression if it is correct. Thanks
 
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So far, so good. You just need to take it one step farther, by replacing (cos2x)2 with (cos4x + 1)/2. At that point you'll have an integral with four terms, and you can split this up into four integrals, each of which is pretty easy.
 
Hey i got the answer (sin4x)/32 + (sin2x)/4 + (3x)/8 + C which seems to be right. Thanks for your help :)
 

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