Đơn giản biểu thức:
a) \(\cos \left( {\alpha - \dfrac{\pi }{2}} \right) + \sin \left( {\alpha - \pi } \right);\)
b) \(\cos \left( {\pi - \alpha } \right) + \sin \left( {\alpha + \dfrac{\pi }{2}} \right);\)
c) \(\cos \left( {\dfrac{\pi }{2} - \alpha } \right) + \sin \left( {\dfrac{\pi }{2} - \alpha } \right) - \cos \left( {\dfrac{\pi }{2} + \alpha } \right) - \sin \left( {\dfrac{\pi }{2} + \alpha } \right)\);
d) \(\cos \left( {\dfrac{{3\pi }}{2} - \alpha } \right) - \sin \left( {\dfrac{{3\pi }}{2} - \alpha } \right) + \cos \left( {\alpha - \dfrac{{7\pi }}{2}} \right) - \sin \left( {\alpha - \dfrac{{7\pi }}{2}} \right)\);
e) \(\cos \left( {\dfrac{\pi }{2} - \alpha } \right) + \cos \left( {\pi - \alpha } \right) + \cos \left( {\dfrac{{3\pi }}{2} - \alpha } \right) + \cos \left( {2\pi - \alpha } \right)\);
f) \(\sin \left( {\dfrac{{5\pi }}{2} - \alpha } \right) - \cos \left( {\dfrac{{13\pi }}{2} - \alpha } \right) - 3\sin \left( {\alpha - 5\pi } \right) - 2\sin \alpha - \cos \alpha ;\)
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g) \(\cos \left( {5\pi + \alpha } \right) - 2\sin \left( {\dfrac{{11\pi }}{2} - \alpha } \right) - \sin \left( {\dfrac{{11\pi }}{2} + \alpha } \right)\).
a) 0; b) 0; c) \(2\sin \alpha \);
d) \( - 2\sin \alpha ;\)
e) 0; f) 0
g) \(2\cos \alpha \)