Help finding a zero of function

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SUMMARY

The discussion centers on finding all zeros of the function f(x) = cos(x) + 3cos(3x) within the interval (-π, π). The user has identified zeros at -π, -π/2, 0, π/2, and π but seeks additional zeros. The conversation highlights the need to factor the function or expand cos(3x) into powers of cos(x) to uncover more zeros.

PREREQUISITES
  • Understanding of trigonometric functions, specifically cosine.
  • Familiarity with the concept of function zeros and their significance.
  • Knowledge of function expansion techniques, particularly Taylor series or trigonometric identities.
  • Graphing skills to visualize function behavior over specified intervals.
NEXT STEPS
  • Learn how to expand cos(3x) using trigonometric identities.
  • Study methods for finding zeros of trigonometric functions.
  • Explore the use of graphing calculators or software to visualize function intersections.
  • Investigate numerical methods for root-finding, such as the Newton-Raphson method.
USEFUL FOR

Students studying calculus or trigonometry, educators teaching these subjects, and anyone interested in solving trigonometric equations and understanding function behavior.

wildcat12
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Homework Statement


I need to find all the zeros of the function f(x)=cos(x)+3cos(3x) on the interval (-pi, pi)


Homework Equations





The Attempt at a Solution


i have found zeros at -pi, -pi/2, 0. pi/2, and pi. Looking at the graph i can see more zeros but i cannot figure out what they are! Anybody know how i can factor this or anything?
 
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Do you know how to expand cos(3x) into powers of cos(x)?
 

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