Matlab ignores pi in a function

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.

Answer 1

[Image Analyst]

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.

[Alex CB]

...I see it now, it seems I'm just an idiot.

Thank you so much, I'm sorry for the troubles.