Toán Lớp 11: Giải phương trình
A) 3 cosx + 4 Sin x = 5cos 2x
b)4 sin x + 3cos x= 4(1+ tan x)-1/cos x
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Toán Lớp 11: Giải phương trình
A) 3 cosx + 4 Sin x = 5cos 2x
b)4 sin x + 3cos x= 4(1+ tan x)-1/cos x
Comments ( 1 )
$x = \frac{\alpha }{3} + \frac{{k2\pi }}{3} $
{\rm{a) }}\\
\sqrt {{3^2} + {4^2}} \cos \left( {x – \alpha } \right) = 5\cos 2x\\
+ \alpha = \arctan \frac{4}{3}\\
\Leftrightarrow \cos \left( {x – \alpha } \right) = \cos 2x\\
\Leftrightarrow \left[ \begin{array}{l}
x – \alpha = 2x + k2\pi \\
x – \alpha = – 2x + k2\pi
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
x = – \alpha + k2\pi \\
x = \frac{\alpha }{3} + \frac{{k2\pi }}{3}
\end{array} \right.
\end{array}\]