Questions about these Trigonometry Graphs involving sin() and cos()

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Discussion Overview

The discussion revolves around understanding the graphs of two trigonometric equations involving sine and cosine functions. Participants explore the nature of these graphs, their critical points, and the implications of certain values within the equations. The focus is on conceptual understanding and analysis of the graphical representations.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant asks for help in understanding the graphs of the equations a sin(x) - b cos(y) = y and a sin(x) + b cos(y) = 1, expressing uncertainty about their shapes.
  • Another participant suggests that finding critical points of the function and understanding their nature is important for analyzing the graphs, comparing it to drawing a phase portrait of a Hamiltonian system.
  • A later reply questions whether an analysis is necessary to proceed with understanding the graphs.
  • Another participant points out that the second graph appears incorrect, noting that if sin(x) < 0, there are no solutions for y, and discusses the symmetry of solutions in the range 0 ≤ x ≤ π, suggesting a periodicity every 2π along the x-axis.
  • This participant also recommends using units of π along both axes for clarity.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and approaches to analyzing the graphs, with some uncertainty about the correctness of the second graph and differing opinions on the necessity of analysis.

Contextual Notes

There are unresolved assumptions regarding the definitions of critical points and the conditions under which solutions exist for the equations. The discussion does not clarify the mathematical steps needed to fully analyze the graphs.

pairofstrings
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TL;DR
a sin(x) - b cos(y) = y
a sin(x) + b cos(y) = 1
Hi.
I have two trigonometric equations whose graphs I am trying to understand.
Here are the equations:
1. a sin(x) - b cos(y) = y; a = 2, b = 2

Web capture_20-8-2023_152359_www.desmos.com.jpeg

2. a sin(x) + b cos(y) = 1; a = 1, b = 1

Web capture_20-8-2023_15261_www.desmos.com.jpeg

My question is why the graphs are the way they are.
What should I do to understand them?
Can anyone explain these graphs?

Thanks for the help.
 
Last edited:
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When you consider level sets ##\{(x,y)\mid f(x,y)=const\}## it is important to find critical points of the function ##f## and understand which kind these critical points are.
So first find the points such that ##df=0##.
It is like drawing a phase portrait of a Hamiltonian system with the Hamiltonian f.
 
Last edited:
Thanks. So, I need to do Analysis first?
 
pairofstrings said:
Thanks. So, I need to do Analysis first?
The second graph looks off to me. You have
$$\cos y = 1 - \sin x$$If ##\sin x <0##, then there are no solutions for ##y##. You have solutions for ##0 \le x \le \pi##, with symmetry about ##x = \frac \pi 2##. Whatever solutions you have in this range are repeated every ##2\pi## units along the x-axis.

It would be better have units of ##\pi## along both axes.

Does that get you started?
 

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