a) \(\left\{-\pi;0;\pi\right\}\)

b) \(\left\{\dfrac{\pi}{4};\dfrac{\pi}{4}\pm\pi\right\}\)

c) \(\left(-\pi;-\dfrac{\pi}{2}\right)\cup\left(0;\dfrac{\pi}{2}\right)\cup\left(\pi;\dfrac{3\pi}{2}\right)\)

d) \(\left(-\dfrac{\pi}{2};0\right)\cup\left(\dfrac{\pi}{2};\pi\right)\)