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[TEX]PT \Rightarrow 1+8sin2x.cos^22x=4sin^2(3x+\frac{3\pi}{4}) \Leftrightarrow 1+8sin2x.cos^22x=2(1-cos(6x+\frac{3\pi}{4})=2+2sin6x \Leftrightarrow 1+8sin2x.(1-sin^22x)=2+2(3sin2x-4sin^32x) \Leftrightarrow 1+8sin2x=2+6sin2x \Leftrightarrow sin2x=\frac{1}{2} \Leftrightarrow \left[\begin{x=\frac{\pi}{12}+k\pi}\\{x=\frac{5\pi}{12}+k\pi}[/TEX]
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