Solve Trig Eqn: Find & Combine 2 Solutions for x

Click For Summary

Discussion Overview

The discussion revolves around finding and combining solutions for a trigonometric equation, specifically the equation \(\cos x + \sin x = 0\). Participants explore different methods of expressing the general solutions and seek to verify their correctness.

Discussion Character

  • Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant presents two expressions for the solutions: \(x = n\pi - \pi/4\) and \(x = (n\pi)/2 + \pi/4\), suggesting they should be equivalent.
  • Another participant agrees with the first expression but challenges the second, providing an alternative form \(x = \frac{2n+1}{2}\pi + \frac{\pi}{4}\) and questioning the validity of the second expression for certain values of \(n\).
  • A subsequent reply clarifies that the second expression should use odd integers for \(n\), which addresses the previous challenge regarding its correctness.
  • Another participant acknowledges this clarification, indicating that both expressions are indeed standard representations of the solutions.

Areas of Agreement / Disagreement

Participants generally agree on the validity of the first expression, while there was initial disagreement regarding the second expression until it was clarified that it applies to odd integers. The discussion reflects a refinement of understanding rather than a definitive resolution.

Contextual Notes

The discussion highlights the importance of specifying the type of integers used in the solutions, which affects the validity of the proposed expressions. There are unresolved aspects regarding the generality of the solutions and their equivalence.

primarygun
Messages
233
Reaction score
0
General solution for a trigonometry equation.
I solved this equation with several method and I found two possible expressions for the answers. They should be exactly the same. Please help me check for them or combine them together to give the one which is more common. Thanks for any ideas.
\cos x + \sin x=0
x=n\pi -\pi/4
x=(n\pi)/2+\pi/4
 
Last edited:
Mathematics news on Phys.org
Your first is correct.
Letting n be some integer, another way to write the solutions is:
x=\frac{2n+1}{2}\pi+\frac{\pi}{4}
Your last equation is incorrect; set n=2.
This says that x=\frac{5\pi}{4} is a root; but this is untrue, since it lies in the 3.quadrant where both the sine and cosine functions are negative.
 
Oh sorry, I missed to state that the n for the second expression is any odd integer. Really sorry.
 
primarygun said:
Oh sorry, I missed to state that the n for the second expression is any odd integer. Really sorry.
In that case, of course, your second equation is just the one I provided; both 1) and 2) are standard ways of writing the solutions
 
Thank you very much.
 

Similar threads

Replies
8
Views
2K
Replies
1
Views
1K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 16 ·
Replies
16
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 19 ·
Replies
19
Views
2K
Replies
1
Views
1K
  • · Replies 19 ·
Replies
19
Views
3K