Solving Trigonometric Equations with Pythagorean Identities

  • Context: Undergrad 
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Discussion Overview

The discussion revolves around solving trigonometric equations using Pythagorean identities, specifically focusing on the equation cos^n(x) - sin^n(x) = 1 for a positive integer n. Participants explore the solutions for various values of n, examining both odd and even cases.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks confirmation on their solution for cos^n(x) - sin^n(x) = 1, referencing the Pythagorean identity cos^2(x) + sin^2(x) = 1.
  • Another participant questions the correctness of the proposed solutions, suggesting that they are incorrect.
  • Some participants propose that the solutions differ based on whether n is odd or even, indicating a pattern in the solutions for each case.
  • One participant claims that x=0 is a solution for all positive n.
  • Another participant mentions that they found solutions by graphing the functions y = cos^n(x) and y = sin^n(x) + 1, noting the intersections of the graphs.
  • There is a discussion about the specific solutions for even and odd n, with some participants suggesting x=k*pi for even n and x=3pi/2 + 2*k*pi for odd n.

Areas of Agreement / Disagreement

Participants express disagreement regarding the correctness of specific solutions. While some agree on the general patterns for odd and even n, the exact solutions remain contested, and no consensus is reached on the validity of the initial claims.

Contextual Notes

Participants acknowledge that their terminology may not be precise, indicating a potential limitation in their explanations. The discussion also reflects varying levels of familiarity with the concepts involved.

BrownianMan
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There's no answer for this in the back of the book and I just want to make sure I did it correctly. If anyone could post their answer, I would appreciate it! Thanks.

Cos^2(x) + sin^2 (x) =1 for every real value of x.(Pythagorean theorem)
What real values of x will be a solution to cos^n (x)- sin^n (x) =1, for a given positive integer n?
 
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x=0.64 + pi/4 +/- 2*pi*n, 0.64 + 3pi/4 +/- 2*pi*n
 


Can you show me how you got those numbers? BTW, they are not correct.
 


What's interesting is that the solutions to x are the same for all odd, and the other set of solutions are equal for all even n.
Your answers are incorrect. Just test them and you'll see.

There is one solution for x that works with all positive n, and that is x=0.
 


Mentallic said:
What's interesting is that the solutions to x are the same for all odd, and the other set of solutions are equal for all even n.
A more accurate way to say this is that there is one set of solutions for all odd integers n, and another set of solutions for all even integers n.
 


Ok, so if n is even x=0 x=k*pi, and if n is odd x=0 x=3pi/2+2*k*pi?
 


BrownianMan said:
Ok, so if n is even x=0 x=k*pi, and if n is odd x=0 x=3pi/2+2*k*pi?
For n even, yes. For n odd, what you have is correct, there is another bunch of solutions. What I did was draw graphs of y = cos^n(x) and y = sin^n(x) + 1, and found the points where the two graphs intersect. The graphs of odd powers of sine and cosine look pretty much like the graphs of sine and cosine.
 


Mark44 said:
A more accurate way to say this is that there is one set of solutions for all odd integers n, and another set of solutions for all even integers n.
Yes, thankyou :smile:
I'm stepping into fields I have yet to learn so my terminology would be questionable at best. I just hope that I can get the point across.
 

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