Solving a Trigonometric Equation: (cos x)^4 = cos (x^2)

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SUMMARY

The equation (cos x)^4 = cos (x^2) presents significant challenges for algebraic solutions due to the differing periodic behaviors of the functions involved. The function y=cos4x is periodic, while y=cos(x^2) does not exhibit a standard periodic pattern, leading to complications as x approaches infinity. While algebraic methods are unlikely to yield a straightforward solution, starting with the known solution x=0 and employing numerical methods such as Newton's method is a recommended approach for further exploration.

PREREQUISITES
  • Understanding of trigonometric functions and their properties
  • Familiarity with periodic functions and their behaviors
  • Knowledge of algebraic methods for solving equations
  • Experience with numerical methods, particularly Newton's method
NEXT STEPS
  • Research the properties of periodic functions in trigonometry
  • Learn about numerical methods for solving equations, focusing on Newton's method
  • Explore advanced algebraic techniques for solving transcendental equations
  • Investigate graphical methods for visualizing solutions to trigonometric equations
USEFUL FOR

Students and educators in mathematics, particularly those involved in algebra and trigonometry, as well as anyone interested in numerical methods for solving complex equations.

Xkaliber
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Hi all,

I was tutoring someone in Algebra III today and encountered a problem that threw me for a loop.

(cos x)^4 = cos (x^2)

Is there a way to solve this algebraically?
 
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Hmm... looks so simple, yet it's so not

I wouldn't know of any algebraic methods to solve this.

y=cos4x is a nice, periodic function like any other standard trig function.

y=cos(x2) doesn't follow this pattern. As [tex]x \rightarrow \pm \infty[/tex] the period of fluctuations [tex]\rightarrow 0[/tex].

If there is an algebraic method to solve this - and I highly doubt it - then it can't be pretty.


Maybe starting with the simple answer x=0 and working from there (I suggest Newton's method :wink:) would be a good start to approach this problem.
 

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