General solution

1. Feb 13, 2005

primarygun

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: Feb 13, 2005
2. Feb 13, 2005

arildno

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.

3. Feb 13, 2005

primarygun

Oh sorry, I missed to state that the n for the second expression is any odd integer. Really sorry.

4. Feb 13, 2005

arildno

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

5. Feb 13, 2005

primarygun

Thank you very much.

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