Pt lượng giác 11

H

happy.swan

[TEX]2sin3x(1 - 4sin^2x) =1 \\ \Leftrightarrow 2sin3x(4cos^2x - 3) =1 \\ \Leftrightarrow 2sin3x(4cos^3x - 3cosx) = cosx (1) \\ \Leftrightarrow 2sin3x.cos3x = cosx \\ \Leftrightarrow sin6x = sin(x + \frac{\pi}{2})[/TEX]

(1): cosx = 0 không là nghiệm
 
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