Toán Lớp 11: 2sin^2.x+3.cos^2.3x
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Toán Lớp 11: 2sin^2.x+3.cos^2.3x
Anh em giải hộ với ạ
Comments ( 1 )
2{\sin ^2}x + 3{\cos ^2}3x\\
= 2.\dfrac{{1 – \cos 2x}}{2} + 3.\dfrac{{1 + \cos \left( {2.3x} \right)}}{2}\\
= 1 – \cos 2x + \dfrac{{3 + \cos 6x}}{2} = \dfrac{5}{2} + \dfrac{{\cos 6x}}{2} – \cos 2x
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