Matlab ignores pi in a function

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Alex CB
Alex CB 2016-1-3
编辑： Walter Roberson 2016-1-4
When I try to use:
syms x; y=3*cos(pi-x^2); diff(y)
it gives
6*x*sin(x^2)
it ignores the pi, giving an incorrect solution and I don't know how to solve it.
It also says that "y=-3*cos(x^2)", ignoring the pi again.
Thanks in advance.

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采纳的回答

Image Analyst
Image Analyst 2016-1-3
Why do you incorrectly think that cos(pi-theta) is not equal to -cos(theta)? It is. Just try plotting some angles on the unit circle to prove it to yourself. So you can use either equation because they are equivalent.
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Alex CB
Alex CB 2016-1-3
...I see it now, it seems I'm just an idiot.
Thank you so much, I'm sorry for the troubles.

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