Google
Câu hỏi: Tính
\(A = \cos \dfrac{\pi }{6}\sin \left( { - \dfrac{\pi }{3}} \right) + \sin \dfrac{\pi }{6}\cos \dfrac{\pi }{3};\)
\(B = \cos \left( { - \dfrac{\pi }{4}} \right)\cos \left({\dfrac{{3\pi }}{4}} \right) + \sin \left({ - \dfrac{\pi }{4}} \right)\sin \left({ - \dfrac{{3\pi }}{4}} \right)\)
\(A = \cos \dfrac{\pi }{6}\sin \left( { - \dfrac{\pi }{3}} \right) + \sin \dfrac{\pi }{6}\cos \dfrac{\pi }{3};\)
\(B = \cos \left( { - \dfrac{\pi }{4}} \right)\cos \left({\dfrac{{3\pi }}{4}} \right) + \sin \left({ - \dfrac{\pi }{4}} \right)\sin \left({ - \dfrac{{3\pi }}{4}} \right)\)
Lời giải chi tiết
\(A = \dfrac{{ - 1}}{2}; B = 0\)
\(A = \dfrac{{ - 1}}{2}; B = 0\)