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[TEX]cos^33x.cos2x-cos^2x=0[/TEX]
[TEX]\leftrightarrow \frac{1}{2}.(1 + cos6x).cos2x - \frac{1}{2}(1 + cos2x) = 0[/TEX]
[TEX]\leftrightarrow (1 + cos6x).cos2x - 1 - cos2x = 0[/TEX]
[TEX]\leftrightarrow cos2x + cos6x.cos2x - 1 - cos2x = 0[/TEX]
[TEX]\leftrightarrow cos6x.cos2x - 1 = 0[/TEX]
[TEX]\leftrightarrow (4cos^32x - 3cos2x).cos2x - 1 = 0[/TEX]
[TEX]\leftrightarrow 4cos^42x - 3cos^2x - 1 = 0[/TEX]
[TẶNG BẠN] TRỌN BỘ Bí kíp học tốt 08 môn
