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How to solve for x in an sin equation?

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aw007
aw007 on 19 Sep 2020
Commented: aw007 on 19 Sep 2020
Hi MATLAB wizards
I am currently trying to solve the following equation; -7sin(x/7)=0 using symbolic algebra and the solve function in MATLAB.
The code that I used is as follows:
syms x
solve( (-7*sin(x/7)),x)
This code returns the value 0, which is one of the solutions, the other one is 7*pi.
So how can I produce both of these solutions?
Any form of help would be appreciated.

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Accepted Answer

John D'Errico
John D'Errico on 19 Sep 2020
Edited: John D'Errico on 19 Sep 2020
No. There are INFINITELY many solutions. So you cannot say you want the OTHER solution. You can simply enough find a positive solution though.
syms x positive
solve( (-7*sin(x/7)),x)
ans =
7*pi

  1 Comment

aw007
aw007 on 19 Sep 2020
Yes you are right there are many solutions.
But this seems to do the trick.
Cheers for the help.

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More Answers (1)

David Hill
David Hill on 19 Sep 2020
[solx,parameters,conditions] = solve(eqn,x,'ReturnConditions',true);

  1 Comment

aw007
aw007 on 19 Sep 2020
yeah that seems to work @David Hill.
But the output is like this:
solx =
7*pi*k
parameters =
k
conditions =
in(k, 'integer')
Not sure if I understand the k and conditions bits.
Here's the code I used in conjunction with yours:
eqn=-7*sin(x/7);
[solx,parameters,conditions] = solve(eqn,x,'ReturnConditions',true)

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