[Toán 10] Lượng giác

B

braga

$$M=\dfrac{(\sin9x+\sin3x)+3(\sin7x+\sin5x)}{\sin6x(3\cos x+\cos3x)}=\dfrac{2\sin6x.\cos 3x+6\sin6x.\cos x}{\sin6x(3\cos x+\cos3x)}=\dfrac{2\sin6x(\cos3x+3\cos x)}{\sin6x(3\cos x+\cos3x)}=\fbox{2}$$
 
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