Pt [imath]\leftrightarrow[/imath] [imath]([/imath]sin^2x[imath]+[/imath]cos^2[imath]x)^2[/imath]-2[imath]sin^2x[/imath] [imath]cos^2x[/imath]+[imath]\dfrac{1}{2}[/imath] (sin2x+sin(4x-[imath]\dfrac{ \pi}{2}[/imath])- [imath]\dfrac{3}{2}[/imath]=0
[imath]\leftrightarrow[/imath] 1-[imath]\dfrac{1}{2}[/imath] [imath]sin^2{2x}[/imath]+[imath]\dfrac{1}{2}[/imath] ( sin 2x+cos4x)- [imath]\dfrac{3}{2}[/imath]=0
[imath]\leftrightarrow[/imath] 1-[imath]\dfrac{1}{2}[/imath] [imath]sin^{2}2x[/imath] +[imath]\dfrac{1}{2}[/imath] sin2x+[imath]\dfrac{1}{2}[/imath](1-[imath]2sin^2{2x}[/imath])- [imath]\dfrac{3}{2}[/imath]=0
[imath]\leftrightarrow[/imath] [imath]-\dfrac{3}{2}[/imath] [imath]\sin^2{2x}[/imath] +[imath]\dfrac{1}{2}\sin2x[/imath]=0
[imath]\leftrightarrow[/imath] sin2x=0 hoặc sin2x= 1/3
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