I've got a plain trigonometric equation.
π/2 can't be the answer, but Wolfram Alpha has a different opinion.
How is it even possible?
Thanks in advance.
Yes, WA can be wrong. I don't know the extent of it, but see here for a simple integral which it gets wrong. The solution, of course, should be log|x| + C, not log(x) + C.
Always check your answers. Even when using a fancy "calculator" like WA.